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New king says family mourns passing of 'cherished sovereign and much-loved mother' after UK's longest-reigning monarch dies aged 96.
The US president Joe Biden and first lady, Jill Biden, said the Queen "was more than a monarch. She defined an era."
"In a world of constant change, she was a steadying presence and a source of comfort and pride for generations of Britons, including many who have never known their country without her.
"An enduring admiration for Queen Elizabeth II united people across the Commonwealth. The seven decades of her history-making reign bore witness to an age of unprecedented human advancement and the forward march of human dignity.
"She was the first British monarch to whom people all around the world could feel a personal and immediate connection-whether they heard her on the radio as a young princess speaking to the children of the United Kingdom, or gathered around their televisions for her coronation, or watched her final Christmas speech or her platinum jubilee on their phones. And she, in turn, dedicated her whole life to their service."
The prime minister, Liz Truss, has said the Queen's death is a "huge shock to the nation and the world".
Truss said the Queen was "the rock on which modern Britain was built and our country has flourished under her reign".
The French president, Emmanuel Macron, said: "Her Majesty Queen Elizabeth II embodied the British nation's continuity and unity for over 70 years."
"I remember her as a friend of France, a kind-hearted queen who has left a lasting impression on her country and her century.
"I remember her as a friend of France, a kind-hearted queen who has left a lasting impression on her country and her century."
Her Majesty was "a monarch with an unwavering sense of duty", said New Zealand's prime minister, Jacinda Ardern, who expressed her country's "deep sadness" at Queen Elizabeth's death.
"People throughout the world will be feeling an acute sense of loss at this time and New Zealanders most certainly share that grief," said Ardern. "The Queen was a much respected constant through unprecedented global change."
Ardern said in a statement: "The Queen was a much loved and admired monarch, whose record reign of 70 years is an absolute testament to her, and her commitment to us all. She was extraordinary.
"People throughout the world will be feeling an acute sense of loss at this time and New Zealanders most certainly share that grief. The Queen was a much respected constant through unprecedented global change."
She offered her "deepest sympathy" to members of the Royal Family on behalf of New Zealand, a Commonwealth country.
"To us she was a much admired and respected monarch, to them she was a mother and grandmother," Ardern said.
Barack Obama, the former U.S. president, said: "Michelle and I were lucky enough to come to know Her Majesty, and she meant a great deal to us.
"Back when we were just beginning to navigate life as President and First Lady, she welcomed us to the world stage with open arms and extraordinary generosity.
"Time and again, we were struck by her warmth, the way she put people at ease, and how she brought her considerable humor and charm to moments of great pomp and circumstance.
"Like so many, Michelle and I are grateful to have witnessed Her Majesty's dedicated leadership, and we are awed by her legacy of tireless, dignified public service.
"Our thoughts are with her family and the people of the United Kingdom at this difficult time."
Flags on the royal palaces have been lowered to half-mast to mark the death of the Queen.
Royal staff attached a notice of Elizabeth II's death to the gates of Buckingham Palace, where crowds were gathering to pay tribute and lay flowers:
George W Bush, the former US president, has said he and his wife Laura "were honoured to have known Her Majesty Queen Elizabeth II."
He said in a statement: "She was a woman of great intellect, charm, and wit.
"Spending time at Buckingham Palace, and having tea with Her Majesty - and her corgis - is among our fondest memories of the presidency.
"Queen Elizabeth ably led England through dark moments with her confidence in her people and her vision for a brighter tomorrow.
"Our world benefitted from her steady resolve, and we are grateful for her decades of service as sovereign. Americans in particular appreciate her strong and steadfast friendship.
"Laura and I join our fellow citizens in sending our heartfelt condolences to the Royal family and the British people."
Sir Ed Davey, leader of the Liberal Democrats in the UK, said: "We are all deeply mourning the profound loss of a great monarch, who served our country so faithfully all her life and who was loved the world over.
"For many people, including myself, the Queen was an ever-fixed mark in our lives.
"As the world changed around us and politicians came and went, the Queen was our nation's constant."
The Irish taoiseach, Micheál Martin, has described The Queen's reign as "one of historic duration, immense consequence and a focus of respect and admiration around the world.
"Her dedication to duty and public service were self-evident and her wisdom and experience truly unique.
"The Queen's passing is indeed the end of an era.
"Her state visit to Ireland in 2011 marked a crucial step in the normalisation of relations with our nearest neighbour.
"That visit was a great success, largely because of the many gracious gestures and warm remarks made by the Queen during her time in Ireland.
"Her popularity with the Irish people was also very evident and clearly made a very positive impact on the Queen.
"In particular, I recall the warmth of the welcome she received from the public in Cork during her walkabout at the English Market."
Bill Clinton, the former US president, has tweeted this tribute:
My thoughts and prayers are with the Royal Family and all the people Her Majesty inspired throughout her lifetime of service. pic.twitter.com/r5pjncyCu8
Sir Keir Starmer, leader of the Labour party, said: "Today, we mourn the passing of a remarkable sovereign.
"It is a deep, private loss for the Royal Family and all our thoughts are with them at this time. The nation shares in their grief.
"We will always treasure Queen Elizabeth II's life of service and devotion to our nation and the Commonwealth; our longest-serving and greatest monarch.
"Above the clashes of politics, she stood not for what the nation fought over, but what it agreed upon. As Britain changed rapidly around her, this dedication became the still point of our turning world.
"So as our great Elizabethan era comes to an end, we will honour the late Queen's memory by keeping alive the values of public service she embodied.
"For 70 years, Queen Elizabeth II stood as the head of our country. But, in spirit, she stood amongst us."
The Belgian prime minister, Alexander De Croo, has paid the following tribute: "Belgium sends its condolences to the British Royal Family and to the British people.
"May HRH Queen Elizabeth II Rest In Peace. For over 70 years, she was a beacon of stability and dignity for the British people."
Nicola Sturgeon, the first minister of Scotland, has also paid tribute.
The death of Her Majesty, Queen Elizabeth is a profoundly sad moment for the UK, the Commonwealth and the world.
Her life was one of extraordinary dedication and service.
On behalf of the people of Scotland, I convey my deepest condolences to The King and the Royal Family. https://t.co/o2XqGJMF2S
Truss said the nation offers King Charles III our "loyalty and devotion".
She ended her statement with the words: "God save the King."
Truss also called for people to support King Charles III "to help him bear the awesome responsibility that he now carries for us all".
Truss said it was "a day of great loss" but that the Queen would leave a great legacy.
Truss added the Queen provided her with stability and strength we needed, "and the very spirit of Great Britain and that spirit will endure".
She adds she was a personal inspiration to her and said she was determined to carry out her duties when she appointed her prime minister earlier this week.
As is traditional, officials brought a notice confirming the Queen's death to the gates of Buckingham Palace.
A large crowd gathered to read it, and Royal Parks staff constructed pens from metal barriers to control the public.
Those gathered broke into the national anthem outside Buckingham Palace with many weeping after the flag was lowered to half mast.
King Charles has made a statement about the death of his mother, Queen Elizabeth.
He said: "The death of my beloved mother, Her Majesty the Queen, is a moment of the greatest sadness for me and all members of my family.
"We mourn profoundly the passing of a cherished Sovereign and a much-loved mother."
A statement from His Majesty The King: pic.twitter.com/AnBiyZCher
Truss said the Queen championed the development of the Commonwealth and "we are now a modern, thriving dynamic nation".
National rail strikes planned for two days next week have been called off by trade unions.
Additional train services are instead expected to be put on to London to allow the public to travel to mourn the Queen.
The RMT general secretary, Mick Lynch, said his union "joins the whole nation in paying its respects to Queen Elizabeth".
As the nation begins a period of mourning, royal residences that are open to the public will be closed.
It is expected bells of Westminster Abbey and St Paul's Cathedral will toll their bells at midday.
It is expected ceremonial gun salutes will be fired in London in Hyde Park and at Tower Hill.
Standing outside the gates of Balmoral as the sombre news of the Queen's death was announced were two accident and emergency nurses from Portsmouth.
Samantha Cole and Tina Ferry had driven over from the Scottish coastal town of Peterhead where they are on holiday after hearing the news on the radio.
Ferry said: "It's a moment in history; it's like Diana. You will always remember where you were when it happened. I hope she hasn't suffered and she passed away peacefully."
Cole, standing beside her in a bright red coat, said she had always loved the royal family and had met Prince Charles when she lived in New Zealand.
She also won tickets in a ballot to stand in Pall Mall in London to celebrate the Queen's 90th birthday. "When you live abroad you realise that the Queen and the royal family are loved everywhere. But you also realise how British you are when things happen, such as royal birthday parties and things like that."
Prime minister Liz Truss is due to make a statement at Downing Street on the Queen's death shortly.
Cardinal Vincent Nichols, the archbishop of Westminster and president of the Catholic Bishops' Conference of England and Wales, has paid tribute to the Queen:
"On 21 April 1947, on her 21st birthday, Princess Elizabeth said, 'I declare before you all that my whole life whether it be long or short shall be devoted to your service.'
"Now, 75 years later, we are heartbroken in our loss at her death, and so full of admiration for the unfailing way in which she fulfilled that declaration.
"Even in my sorrow, shared with so many around the world, I am filled with an immense sense of gratitude for the gift to the world that has been the life of Queen Elizabeth II.
"At this time, we pray for the repose of the soul of Her Majesty. We do so with confidence, because the Christian faith marked every day of her life and activity."
Sir Tony Blair, the UK prime minister between 1997 and 2007, said: "We have lost not just our monarch but the matriarch of our nation, the figure who more than any other brought our country together, kept us in touch with our better nature, personified everything which makes us proud to be British."
The Commons Speaker, Sir Lindsay Hoyle, said the Queen's death was a "terrible loss for us all", adding: "We will miss her beyond measure."
He said: "For all of us, the Queen has been a constant presence in our lives - as familiar as a member of the family, yet one who has exercised a calm and steadying influence over our country. Most of us have never known a time when she was not there.
"Her death is not only a tragedy for the royal family, but a terrible loss for us all.
"During her 70 years on the throne - and even before that, as a teenager, reassuring and engaging with children and families disrupted by the Second World War - she has given our lives a sense of equilibrium."
Tributes are now coming in for the Queen from around the world. Sir John Major, the former UK prime minister, said: "For 70 years Her Majesty The Queen devoted her life to the service of our nation and its wellbeing.
"In her public duties she was selfless and wise, with a wonderful generosity of spirit. That is how she lived - and how she led.
"For millions of people - across the Commonwealth and the wider world - she embodied the heart and soul of our nation, and was admired and respected around the globe.
"At this moment of deep sadness, I believe we all stand hand in hand with the royal family as they grieve the loss of one so loved.
"For we have all lost someone very precious to us and, as we mourn, we should be grateful that we were blessed with such an example of duty and leadership for so very many years."
The Lord Speaker, Lord McFall of Alcluith, said "the nation and the whole Commonwealth is united in deep mourning."
"On behalf of the House of Lords, I extend our thoughts and prayers, first and foremost, to His Majesty the King and the other members of her family.
"Her Majesty's supreme dedication to public service is unparalleled and her legacy will be eternal. Today the nation should reflect on the service she gave to the Crown and to her people, and to give thanks for her life."
Charles Michel, president of the European Council, has tweeted this tribute:
Our thoughts are with the royal family and all those who mourn Queen Elizabeth II in the UK and worldwide.
Once called Elizabeth the Steadfast, she never failed to show us the importance of lasting values in a modern world with her service and commitment. pic.twitter.com/NZj3qcyhU7
The Prince of Wales is now king and head of state, and the Duchess of Cornwall is now queen consort.
Queen Elizabeth II, the longest-reigning monarch in British history, has died.
Prince Charles, heir to the throne since the age of three, is now king, and will be officially proclaimed at St James's Palace in London as soon as practicably possible.
Flags on landmark buildings in Britain and across the Commonwealth were being lowered to half mast as a period of official mourning was announced.
As Queen of the UK and 15 other realms, and head of the 54-nation Commonwealth, Elizabeth II was easily the world's most recognisable head of state during an extraordinarily long reign.
Coming to the throne at the age of 25, she successfully steered the monarchy through many squalls during decades of turbulent change, with her personal popularity providing ballast during the institution's more difficult times.
Fifteen prime ministers served her, attesting to her extraordinary knowledge, experience of world affairs and mastery of political neutrality.
There were undoubted low points, but the mass outpouring of affection demonstrated on her silver, golden and diamond jubilees testified to the special place she held in the nation's heart.
And she regarded her role as a life-long duty. In her silver jubilee message in 1977, the Queen said: "When I was 21, I pledged my life to the service of our people, and asked for God's help to make that vow. Although that vow was made in my salad days, when I was green in judgment, I do not regret nor retract one word of it."
The Prince of Wales becomes king immediately, though his official coronation will not take place for some time.
It is expected Charles will hold his first audience with the prime minister some time today.
A formal proclamation will be made as soon as practicably possible at an accession council at St James's Palace.
Members of the privy council, which advises the monarch on matters of state, will be summoned. Traditionally invitees include members of the House of Lords, the lord mayor, aldermen and other leading citizens of the City of London, as well as the high commissioners in London of member nations of the Commonwealth.
Related: Prince Charles becomes king after death of mother, Queen Elizabeth II
The Queen's funeral will, according to tradition, be a state funeral, a rare honour mostly reserved for the sovereign.
The only monarch not to be given a state funeral in the last 295 years was Edward VIII, who abdicated.
State funerals have, on rare occasions, by order of the monarch and by a vote in Parliament providing the funds, been held for distinguished figures including Sir Isaac Newton, Lord Nelson, the Duke of Wellington and wartime prime minister Sir Winston Churchill.
The last state funeral in the UK was Churchill's in 1965 and the last state funeral for a sovereign was for the Queen's father, George VI, in 1952.
State funerals are the responsibility of the Earl Marshal and the College of Arms, and are publicly funded.
The official plans for her death, codenamed London Bridge, will now be activated.
The nation and other countries of which she was head of state will enter a 10-day period of mourning.
Details of her state funeral, accorded to monarchs, will be announced in due course, after being officially signed off by the king.
Tradition dictates that the framed formal announcement of her death is affixed to the railings at Buckingham Palace.
Ceremonial gun salutes will be fired as a mark of respect as royal residences open to the public will close.
Sam Knight wrote about the plans:
Related: 'London Bridge is down': the secret plan for the days after the Queen's death
Here is the announcement from the royal family.
The Queen died peacefully at Balmoral this afternoon.
The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow. pic.twitter.com/VfxpXro22W
The flag at Buckingham Palace was lowered to half mast at 6.30pm.