Prime Minister Anthony Albanese will host diplomats from more than 20 Commonwealth nations to commemorate the life and service of the Queen.
Commonwealth ambassadors and high commissioners will meet the prime minister at his Canberra residence, The Lodge, on Tuesday morning for a memorial service.
Deputy Prime Minister Richard Marles, Foreign Minister Penny Wong, Finance Minister Katy Gallagher and Pacific Minister Pat Conroy are also expected to attend.
The prime minister said it was important for his government to engage with fellow Commonwealth countries and pay tribute to the Queen.
"This is a time for unity of Australia as a nation, a time where we are grieving and acknowledging the contribution of Queen Elizabeth II as our head of state for 70 years," he told reporters in Canberra on Monday.
"We commemorate, as well, King Charles III and his appointment as Australia's head of state."
Mr Albanese is preparing to travel to London later this week along with Governor-General David Hurley to attend the state funeral for the late monarch.
When he returns, Australia will have a day of mourning on September 22 which will include a national memorial service at Parliament House.
The short notice of the public holiday sparked concern among medical professionals about the impact on planned elective surgeries.
A spokesperson for Ramsay Health Care, which manages a number of private Victorian hospitals, told AAP while some services such as day programs and infusions would be rescheduled, surgeries would go ahead.
"In recognition of the severe impact of COVID-19 disruptions on elective surgery over the past two years, we will proceed with some surgical and procedural lists as planned ... where there is capacity to do so," the spokesperson said.
Meanwhile, Victorian MPs will be re-sworn and a condolence motion held on Tuesday before state parliament adjourns to next week as a mark of respect.
The re-swearing of senior public office holders and members of parliament following the death of the reigning monarch is unique to Victoria's constitution.