Australia's Governor-General David Hurley has described the sense of dread he felt when his phone rang in the early hours to inform him of the death of Queen Elizabeth II.
"It was news that I desperately did not want to hear," he told the nation in a televised address on Friday night.
The 96-year-old monarch died overnight at Balmoral Castle in Scotland after a record seven-decade reign, bringing a second Elizabethan age to a close.
"We mourn her passing, we are grateful that we have witnessed, and benefited from, her remarkable life," Mr Hurley said. "May she rest in peace."
Prime Minister Anthony Albanese and UK Prime Minister Liz Truss spoke by phone on Friday.
"The leaders shared their condolences following the passing of Her Majesty the Queen, and agreed she had touched the lives of many, both in Australia and the UK," a Downing Street spokesperson said.
Tributes flowed in Australia throughout the day with Mr Albanese, former prime ministers and the opposition leader all paying homage to her life and legacy.
Around the country people laid flowers, signed condolence books and shared their memories of Elizabeth Alexandra Mary Windsor, whose reign began at the age of 25 in February 1952.
A 96-gun salute was fired from the forecourt of Parliament House in Canberra on Friday evening - one round for each year of the Queen's life at 10-second intervals.
Flags flew at half-mast and the Sydney Opera House sails and other buildings around the county were lit up on Friday night in her honour.
"An historic reign and a long life devoted to duty, family, faith and service has come to an end," Mr Albanese said on Friday.
"The government and the people of Australia offer our deepest condolences to the royal family, who are grieving for a beloved mother, grandmother and great-grandmother - the person whom for so long was their greatest inner strength."
Mr Albanese said that "from her famous first trip to Australia, the only reigning sovereign to ever visit, it was clear Her Majesty held a special place in her heart for Australia".
The Queen travelled to Australia 16 times, the last in 2011 for the Commonwealth Heads of Government Meeting in Perth.
Opposition Leader Peter Dutton said the Queen brought a stabilising force to the world.
"She has been such a significant part of our lives and the stability of our country, of our system of democracy - not just here - but around the world," he said.
Former prime minister Paul Keating said her public service was a "lesson in dedication".
"Her exceptionally long, dedicated reign is unlikely to be repeated; not only in Britain but in the world generally."
Former prime minister John Howard said he would look back on his meetings with the Queen during his years in power with great affection.
"She had what seemed to me to be a deep curiosity about Australia. She understood different features of Australian life," he said.
Former prime minister Julia Gillard was on a long-haul flight when the Queen died and did not hear the "terribly sad" news until disembarking on Friday evening.
"The Queen has been a powerful presence for as long as many of us can remember," she said in a statement.
"The Queen will be remembered as an extraordinary monarch who witnessed - and influenced - the trajectory of modern history."
Acting Primate of the Anglican Church of Australia, Archbishop Philip Freier, said the Queen was admired and respected across the nation.
"As a frequent visitor to Australia the Queen had a special place in the hearts of Australians and she leaves behind a truly extraordinary legacy, having touched the lives of so many," he said.
Under constitutional law, King Charles III immediately became king when his mother died and is Australia's new head of state. A proclamation ceremony will be held in Canberra on Sunday.
Mr Albanese and Mr Hurley are expected to travel to London on Thursday for the Queen's funeral, which could be held on September 19.
A national memorial service will be held in Australia after they return.