Prime Minister Anthony Albanese says it is a day of profound grief and sadness, as Australia mourns the death of Queen Elizabeth II, aged 96.
"With the passing of Queen Elizabeth II, an historic reign and a long life devoted to duty, family, faith and service has come to an end," Mr Albanese said.
"There is comfort to be found in Her Majesty's own words: Grief is the price we pay for love."
The flag at Parliament House will be lowered to half-mast this morning.
Federal parliament will not sit as scheduled next week, and will not return for at least a fortnight.
"This is a loss we feel deeply in Australia," Mr Albanese said.
"Queen Elizabeth II is the only reigning monarch most of us have known, and the only one to ever visit Australia.
"Through the noise and turbulence of the years, she embodied and exhibited a timeless decency and enduring calm.
"From her first trip here, it was clear Her Majesty had a special place in our hearts, and we, in hers."
In the coming days, the Prime Minister and Governor-General David Hurley will travel to London to meet King Charles III.
The Governor-General said the Queen had served with distinction for seven decades.
"When I reflect on my own memories - and she was my Queen my entire life - I think of Her Majesty's dignity and her compassion, her dedication and her work ethic, and her selfless and unwavering commitment to those of whom she served - to us," he said.
Opposition Leader Peter Dutton said there had never been a more dignified monarch, dutiful leader or decent human in modern history than the Queen.
Mr Dutton said a "comforting warmth" had left the world.
At dusk, a gun salute will occur at Parliament House, with one round fired for each year of the Queen's life at 10-second intervals.
Condolence books will be opened at Parliament House, Government House (the Governor-General's residence in Canberra) and the website of the Department of Prime Minister and Cabinet.
They will remain open for a fortnight.
Tomorrow, the Governor-General, the Prime Minister, Opposition Leader and other government ministers will lay wreaths at the Queen's Terrace in Parliament House.
More to come.