The declaration was made by the Governor General of Australia, David Hurley, in Parliament in Canberra. A series of proclamation ceremonies will also take place at the state legislatures in the country on Sunday.
A national day will be held on September 22, after Prime Minister Anthony Albanese returned from Britain and attended the Queen’s funeral. A memorial service will also be held on the same day, which has become a temporary holiday.
As Head of State, Queen Elizabeth II has made 16 visits to Australia.
“From her famous first visit to Australia, it was clear Her Majesty had a special place for Australia.
“After 15 more tours, crowds across our country cheered and confirmed she holds a special place among us.”
In 1999, Australia held a referendum to remove the Queen as head of state, but it was rejected.
On Friday, Sydney’s iconic Opera House was lit up in a tribute to the Queen.
Neighboring New Zealand also formally declared King Charles III as head of state on Sunday in a televised ceremony.
Prime Minister Jacinda Ardern said Queen Elizabeth had served the people of New Zealand for 70 years with an unwavering duty.
“For the majority of New Zealanders, she is the only monarch we know, so her death ushers in a time of change,” Ardern said.
“King Charles has had a long-standing affection for Aotearoa New Zealand and has consistently demonstrated his deep concern for our country,” she added. “And when one chapter ends, another begins.”
Canada’s parliament will open on Thursday so members can pay their respects to Queen Elizabeth II, Prime Minister Justin Trudeau said on Twitter on Saturday.
Prime Minister Trudeau added that the Canadian parliament will also delay its opening by a day. “To accommodate Her Majesty’s funeral, we will delay the start of the session by one day to September 20,” Prime Minister Trudeau said.