LIVE - Updated at 15:07
Total number of confirmed UK Omicron cases now at 37,101; Irish officials say 52% of cases estimated to be the Omicron variant.
The UK reported more than 12,000 further confirmed cases of the Omicron variant of the coronavirus in the latest daily figures provided by health authorities on Sunday.
The UK Health Security Agency said on Twitter there had been an additional 12,133 confirmed cases of Omicron over the previous 24 hours, taking the total number of confirmed cases to 37,101.
#OmicronVariant latest information
12,133 additional confirmed cases of the #Omicron variant of COVID-19 have been reported across the UK.
Confirmed Omicron cases in the UK now total 37,101. pic.twitter.com/fKJ87MEkpM
The first case of Omicron was announced on 24 November by South Africa, with the first positive sample dating back to 9 November. Since then it has been found in multiple countries around the world, including the UK, where the first cases were reported on 27 November in two people in England with links to travel to southern Africa.
But the first known case is not the same as the first infection. Echoeing the views of other experts, Prof Oliver Pybus, the co-director of the Oxford Martin school's programme on pandemic genomics, said that, in his reading, Omicron has likely been circulating for at least a month.
Sri Lanka will require the showing of a Covid-19 vaccination certificate compulsory for entry to public places starting from New Year's Day, in a renewed attempt to prevent another spike in infections.
Tourism minister Prasanna Ranatunga made the announcement on Sunday in an abrupt switch from the gradual ending of restrictions put into place after the country was confronted with a third wave of infections in April caused by the Delta variant.
Ranatunga said health officials were drawing up arrangements on implementing the decisions, Reuters reported.
Omicron is now the dominant strain of Covid-19 in the Republic of Ireland, according to authorities, who said that recent measures had slowed down the spread somewhat.
As Ireland's Department of Health confirmed that there had been 5,124 new cases of Covid-19, it said that it an estimated 52% of reported cases are as a result of the Omicron variant.
Chief Medical Officer Dr Tony Holohan told RTE News: "It has taken less than two weeks for Omicron to become the dominant strain of Covid-19 in Ireland, revealing just how transmissible this variant is.
The deputy first minister of Northern Ireland's power sharing executive, Michelle O'Neill, has warned that Omicron will hit the community there "like a ton of bricks".
She said that modelling presented to her and other officials suggested that, in a worst-case scenario, it could be facing 30,000 Omicron cases a day.
Covid-19 related staff absences will affect all sectors in the UK including the health services, education, police, transport and key national infrastructure unless transmission is not reduced, a leading public health expert has warned.
Sir Jeremy Farrar, who resigned in November from a national advisory body in disagreement with the government's approach, said on Twitter today that Covid-19 and the highly infectious new Omicron variant was not just health issue but also an "economic, education, national infrastructure issue even a security issue."
Like other healthcare experts and practitioners, Farrar has been picking up on a report on Saturday in the Health Service Journal (HSJ) that the number of National Health Service (NHS) staff in London absent due to covid has more than doubled in four days.
One in three of the workforce would be absent by New Year's Eve if the growth rate continues, it added.
The biggest problem facing the #NHS right now is staff absence.
A hospital bed is no good without a team to look after the patient.
Staff absence forecasts reveal 'bleak picture' for coming weeks | News | Health Service Journal https://t.co/HHdofAT9MF
Thousands of peaceful protesters demonstrated in central Brussels on Sunday for a third time against reinforced Covid-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant.
A strong police presence was deployed on the streets in anticipation of the crowds, given how previous protests had sometimes descended into violence, arrest and injury.
The marchers - some with placards reading "free zone", "I've had my fair dose" and "enough is enough" - came to protest against the government's strong advice to get vaccinated, and included Belgian healthcare workers who will have a three-month window in which to get vaccinated against coronavirus from 1 January or risk losing their jobs.
On Sunday, the Brussels-based European Commission agreed with Pfizer-BioNTech to accelerate the delivery of vaccines starting in a few weeks. The pharmaceutical giant will deliver an additional 20m doses from January to March to European Union member states.
The Belgian protest comes one day after similar protests in other European capitals, including Paris and London.
A Brussels demonstration last month spiralled into violence as several hundred people started pelting police, smashing cars and setting garbage bins ablaze. Police responded with teargas and water cannon.
New York state has reported that nearly 22,000 people tested positive for Covid-19 on Friday - eclipsing Thursday for the highest single-day total for new cases since testing became widely available. Amid fears over the new Omicron variant of the coronavirus, more than half of the positive results were in the city.
The Rockettes on Friday cancelled remaining performances of the Radio City Christmas Spectacular, citing "increasing challenges from the pandemic". Saturday Night Live taped without an audience and with reduced crew. Lines at some testing sites stretched around the block and at-home tests remained hard to find or pricier than usual.
But new hospitalisations and deaths are averaging well below their spring 2020 peak and even where they were this time last year, during a winter wave that came as vaccinations were just beginning, city data shows.
In England, the NHS was given a target to administer 1m vaccine shots a day to beat Omicron.
And on Saturday they were getting pretty close, as our political editor Heather Stewart tweets:
Looks like the public are really listening to the call to get their boosters (NB this is England only). https://t.co/R8z5w8jHpN
Queues to get booster shots were long again on Sunday, with people lining up to get their jabs at the Wembley Stadium vaccination site:
Omicron will hit Northern Ireland "like a ton of bricks", the deputy first minister, Michelle O'Neill has warned.
PA Media reports that O'Neill said modelling presented to Stormont ministers suggests that in a worst-case scenario, the region could be facing 30,000 cases a day.
Executive ministers are involved in discussions about the situation ahead of a formal meeting on Wednesday, when it is expected new restrictions to be applied after Christmas will be announced.
O'Neill told the BBC Sunday Politics programme that ministers will act before then if it is deemed necessary.
She said: "In terms of what we know, we know that this is going to hit us like a ton of bricks.
"We know that by the end of the year this will be the dominant strain of Covid, we know that we will peak in the middle of January, we know it is going to spread rapidly.
"What we don't yet know is the impact in terms of our hospital situation, and we expect to understand that a bit more tomorrow and that is when we will engage again.
"Then we decide when to intervene and what is the appropriate intervention."
Americans have been urged to get their booster shots and continue to wear masks by the US infectious disease expert Anthony Fauci.
Fauci said on Sunday that the easily transmissible Omicron variant is "raging through the world".
According to Reuters, he also cautioned that travelling will increase the risk of infection, even among vaccinated people, in an interview with NBC's Meet the Press.
French education minister Jean-Michel Blanquer has said on BFM television that the government has no plans to extend the Christmas school holidays because of the rapid spread of the Omicron coronavirus variant.
Some European countries have brought Christmas holidays forward, and French conservative presidential candidate Valérie Pecresse has called for an extension of them in order to help ensure any infections caught over year-end holidays are discovered before children return to school.
Israel's prime minister has warned citizens against the spread of the new, highly infectious variant of coronavirus on Sunday and urged them to vaccinate.
Naftali Bennett told ministers that there was already community transmission of the omicron variant in Israel and a rise in the country's coronavirus infection rate. He called the omicron variant "very infectious".
"It must be understood that the collective and national protection that the state provides is not enough," Bennett said at the start of the weekly Cabinet meeting.
He urged Israelis that "every citizen must see to themselves, their family, and their children. Don't rely on the neighbours to vaccinate themselves and their child. It won't help much."
Israel rolled out a world-leading vaccination campaign, and more than 4.1 million of Israel's 9.3 million people have received a third dose of the Pfizer/BioNTech vaccine. The country's health ministry has reported at least 134 confirmed cases of the omicron variant since its emergence in late November.
The British government's health minister, Sajid Javid, has made clear that tougher Covid restrictions could be imposed in England before Christmas, after the government's Sage committee warned that hospitalisations could peak at between 3,000 and 10,000 a day unless action is taken.
Javid acknowledged that data about the Omicron variant remained incomplete - but suggested it might be necessary to make decisions before a full picture is available.
Asked to rule out new measures pre-Christmas, he said: "We are assessing the situation; it's very fast-moving," adding, "There's a lot of uncertainty, there are gaps in the data, but we must work with the data we've got, we mustn't let perfection be the enemy of the good."
Speaking on the BBC's Andrew Marr Show, Javid stressed that it was already clear that Omicrom spread very quickly, adding that there were likely to be many more cases than official data is showing.
In minutes published this weekend, the Scientific Advisory Group for Emergencies (Sage) urged the government to reintroduce "more stringent measures . very soon", warning that cases were set to reach between 600,000 and 2 million a day by the end of the month if action was not taken immediately.
The Kremlin is convinced that the World Health Organization (WHO) will recognise Russia's flagship Sputnik V Covid-19 vaccine within a few months, the Interfax news agency cited Kremlin spokesperson Dmitry Peskov as saying on Sunday.
The Kremlin on Tuesday said Russia had still not handed over all the information needed for the vaccine to be approved by the WHO because of differences in regulatory standards.
The head of Germany's domestic intelligence agency has been talking about the potential for serious acts of political violence coming from the country's anti-vaccine movement, in which organised far right activists are increasingly involved in some regions.
Thomas Haldenwang, the president of the Federal Office for the Protection of the Constitution, said in an interview with journalists from the Funke media group: "It is true that there is a difference between talking about violence and committing it,"
But he cited the case of a 49-year-old German citizen who was arrested in September on suspicion of shooting dead a petrol station worker who refused to serve him while he was not wearing a mask.
Asked about possible murder plots in future, he replied: "With violence-oriented rightwing extremists and in the radicalised corona protest milieu, no scenario can be ruled out."
Mass lateral flow testing cut the number of people needing hospital treatment for Covid by 32% and relieved significant pressure on the NHS when the measures were piloted last year, a study in north-west England has shown.
Liverpool conducted the first city-wide testing scheme using rapid antigen tests in November last year, amid debate about whether or not lateral flow tests (LFTs) were accurate enough to detect the virus in asymptomatic carriers.
It expanded the project to cover the whole of the Liverpool region, offering people LFTs whether or not they had symptoms. Key workers did daily tests before going to work to show they were not infectious.
Fresh analysis has shown that it was more successful than Liverpool's scientists and public health teams had anticipated, after they compared Covid cases and outcomes in the region with other parts of England.
Shops in the Netherlands were closed and people's Christmas plans were in disarray as the country began a lockdown on Sunday aimed at limiting an expected Covid-19 surge caused by the rise of the Omicron variant.
Prime minister Mark Rutte announced the sudden shutdown on Saturday evening, ordering the closure of all but the most essential stores, as well as restaurants, hairdressers, gyms, museums and other public places from Sunday until at least 14 January.
The news came as a shock to many Dutch people as they headed into the Christmas and New Year period, Reuters reports. Many people rushed out on Saturday to stock up on presents and food and to get a last-minute haircut.
Hospitality workers demanded compensation for lost income in the holiday season, while gym owners stressed the importance of exercise during a health crisis.
"Closing all bars and restaurants in such an important month is incredibly painful and dramatic. We need compensation and an exit strategy", the Dutch association for hospitality services said.
All schools will close a week early for the Christmas break on Monday and will remain shut until at least 9 January, while households are recommended to receive no more than two visitors and gatherings outside are also limited to a maximum of two.
Coronavirus infections in the Netherlands have dropped from record levels in recent weeks after a night-time lockdown was put in place late last month. But cases involving the Omicron variant have increased rapidly since the beginning of December and the strain is expected to become dominant before the end of the year.
This will pose a big problem for hospitals, which have been cancelling regular care for weeks as they try to avoid running out of beds due to the high numbers of Covid patients on their wards.
Spain's prime minister has called on the country to keep its guard up as the Omicron variant spreads and as the number of cases per 100,000 people in Spain rose to 511, writes the Guardian's Sam Jones in Madrid.
"Although the incidence is still lower than in neighbouring countries, it isn't good because it's a clear and real warning of the threat to the health of our fellow Spaniards and as such, it must compel us to intensify our actions as the virus grows," Pedro Sánchez said in a televised address on Sunday morning.
The prime minister said Spain's regional presidents would attend an online emergency meeting on Wednesday afternoon to discuss next steps.
Esta nueva ola de #COVID19 tiene características distintas y nos afecta en circunstancias muy diferentes. Con más contagios, las cifras de hospitalización y ocupación de UCIs son inferiores.
Las vacunas funcionan. Perseveremos: vacunación, vacunación y vacunación. pic.twitter.com/0KovnX9Mm5
"The virus is still among us and fighting it must continue to be a priority for all the authorities," said Sánchez. "But I would urge people to remain calm and confident. We have come through the most painful part of this together and we will come through this by protecting the health and lives of our fellow citizens."
However, he said that the situation appeared far better than a year ago: "It's worth pointing out that the characteristics of this new wave are different. Although the infection numbers are higher, our hospitalisation and ICU admission figures are lower than last year. The first conclusion that should be drawn is that the vaccines work."
To date, 89.7% of those aged over 12 in Spain have received two doses of the vaccine, and the rollout to children under 12 began earlier this week.
Piers Corbyn, a leading Covid-19 denier, has been arrested on suspicion of encouraging people to burn down MPs' offices.
The Metropolitan police said a man in his 70s - whom it did not name - was arrested in Southwark, south London, in the early hours of Sunday.
"The arrest relates to a video posted online in which people were encouraged to burn down MPs' offices," the force said. Earlier, the Met said it was assessing a video that appears to show Corbyn, 74, calling for MPs' offices to be burned down.
The video, shared on social media, shows Corbyn, a prominent anti-lockdown protester and brother of the former Labour leader Jeremy Corbyn, criticising politicians who voted for Covid restrictions.
After urging the crowd to "hammer to death those scum who have decided to go ahead with introducing new fascism", Corbyn appears to tell a crowd in the video: "You've got to get a list of them . and if your MP is one of them, go to their offices and, well, I would recommend burning them down, OK. But I can't say that on air. I hope we're not on air."
Most of the parties he had planned to go to have been cancelled or scaled back and he wont't be having the same number of hugs with his elderly mother, Britain's health minister has told the BBC.
"It's time to be more cautious. We know this thing is spreading rapidly," Sajid Javid told broadcaster Andrew Marr.
He was not ruling out a new "circuit breaker" increase in restrictions coming in even before Christmas.
"There are no guarantees in this pandemic. At this point, we just have to keep everything under review."
Iran has detected its first case of infection by the new omicron variant of the coronavirus, state TV reported on Sunday.
The announcement comes as the variant spreads around the globe less than a month after scientists alerted the World Health Organization to the concerning-looking version.
Iran has vaccinated 60% of its population of roughly 85 million people with two doses of coronavirus vaccines.
The coronavirus has killed more than 131,000 people in Iran, the worst fatality rate in the Middle East. On 24 August alone, 709 people died of the illness. The number of deaths has decreased in recent months due to the vaccination, experts say.
Iran accelerated vaccinations in recent weeks. More than 50 million Iranians have received their second shots, and 3.5 million have received a third jab.
The UK health minister, Savid Javid, also came under pressure on Sky News to say whether the government would implement stronger restrictions, in line with what experts have been recommending.
Parliament would be recalled if this was necessary, he said.
"We have shown in the past that we will do what is necessary, but it has got to be backed up by the data," he added, though he insisted that the UK was in a "different place" in terms of the defences that vaccines and new treatments could provide.
He also faced questions about whether the public would follow any new rules - particularly in England - given recent allegations about the apparent flouting of pandemic restrictions during 2020 by staff at Downing Street, other departments and in the governing Conservative party.
"I believe the British people will respond in the same way as they have done throughout this pandemic, where if they understand the issues, know just how important it is for their families, they will respond accordingly," said Javid.
New restrictions in England that would governing social distancing and household mixing are "inevitable", the mayor of London, Sadiq Khan, has said.
"If we don't bring in restrictions sooner rather than later you are going to see even more positive cases and potentially public services like the NHS (National Health Service) on the verge of collapsing if not collapsing," he said in an interview on the BBC's Andrew Marr Show.
Britain's health minister, Sajid Javid, has said unvaccinated people are "taking up hospital beds" that could be used for someone else.
Speaking on Sky News, Javid said 10% of the population - more than 5 million people - still had not received their jabs, and about nine out of 10 of those needing the most care in hospital were unvaccinated.
He added: "I just cannot emphasise enough the impact that they are having on the rest of society."
"They must really think about the damage they are doing to society by . they take up hospital beds that could have been used for someone with maybe a heart problem, or maybe someone who is waiting for elective surgery."
"But instead of protecting themselves and protecting the community they choose not to get vaccinated. They are really having a damaging impact and I just can't stress enough, please do come forward and get vaccinated."
UK government ministers have been accused of failing to protect the most vulnerable people from rising Covid cases after it emerged in England and Wales that people with blood cancer account for a higher proportion of coronavirus deaths than earlier in the pandemic.
With daily case numbers at record highs as a result of the Omicron variant, charities warn that people with suppressed immune systems who had been helped to shield at the start of the pandemic felt obliged to put themselves at risk at work, were confused about how to access treatments and less likely to have protection from vaccines.
More than 3,000 people with blood cancer - just over one in 100 of all those who have the disease in England and Wales - have died of Covid, according to analysis of official data by Blood Cancer UK.
This is despite these patients having spent long periods shielding to avoid contact with the virus.
Related: Rising number of blood cancer patients dying of Covid in England and Wales
Large swathes of England, including several major cities, have no vaccination walk-in centres, it has emerged, sparking fears the government will miss its target of offering all adults a booster jab by the end of this month.
As the tide of Omicron cases surges, thousands seeking a third vaccination without having to wait days or weeks for an appointment are driving miles to neighbouring counties.
People without transport and those for whom a walk-in centre is the only option - because they do not have a GP or an NHS number - have no access to Covid booster jabs.
Several cities, including Norwich, Peterborough and York, have no walk-in centres. And there are no walk-in boosters available in entire counties, including Oxfordshire, Hampshire and Buckinghamshire, although some offer third doses for people with weakened immune systems.
Hello and welcome to coverage of all Covid-19 related news, internationally and here in the UK, where the scale of the threat posed by the Omicron variant has been laid bare by government scientists who warned that there are now hundreds of thousands of infections every day in Britain.
They warned daily number could reach between 600,000 and 2 million by the end of the month if new restrictions are not brought in immediately.
In other developments:
. Nations across Europe moved to reimpose tougher measures to stem a new wave of Covid infections, with the Netherlands leading the way by imposing a nationwide lockdown.
. Germany is tightening restrictions on travel from the UK in an attempt to curb the spread of the Omicron variant.
. The World Health Organization reported on Saturday that the Omicron variant of the coronavirus has been detected in 89 countries, and Covid cases involving the variant are doubling every one-and-a-half to three days in places with community transmission and not just infections acquired abroad.
. Kamala Harris has conceded that the Biden administration was blind to the emergence of the Delta and Omicron variants of Covid-19, and said she fears "misinformation" over vaccines will prolong the pandemic well into a third year in the US.
. Australia's federal health minister has said it is unlikely the country will follow the Netherlands and impose significant lockdowns to suppress surging Omicron infections, although the deputy chief medical officer, noted that the new variant was highly transmissible
This is Ben Quinn in London. You can flag up any news that we should be aware of on Twitter at @BenQuinn75 or email me.
The reimposition of new Covid restrictions in England have been cited as one of the reasons for the resignation of a key UK government minister.
The departure of Lord Frost, who was the government's 'Brexit' minister in charge of overseeing the continuing difficulties surrounding Britain's departure from the European Union, presents yet another political setback for the increasingly beleaguered prime minister.
It comes after month in which one after another has popped up like - as one minister put it - a "bad advent calendar."
Conservative MPs were already warning Boris Johnson that he must regain control of the government to survive as leader until the next election when it emerged on Saturday night that Frost is to leave the government after frustrations over Brexit negotiations and broader concerns over the government's Covid policies and tax increases.
The peer has been vocal in recent weeks about his concerns over tax increases and the reimposition of Covid restrictions. He is understood to have spoken out against a rise in national insurance to pay for health and social care spending.
He also has concerns about plan B Covid measures, which provoked the largest Tory rebellion under Johnson's leadership.
At a conference last month he said:
I am very happy that free Britain, or at least merry England, is probably now the freest country in the world as regards Covid restrictions. No mask rules, no vaccine passports, and long may it remain so.