Queen Elizabeth II has died, aged 96, at Balmoral.
A statement from Buckingham Palace on Thursday (Friday morning AEST) confirmed her 70-year reign had come to an end.
"The Queen died peacefully at Balmoral this afternoon," Buckingham Palace said.
"The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow."
As news of the monarch's death ricocheted around the world, thousands of people gathered outside Buckingham Palace on a rainy London night to pay their respects.
There were similar scenes outside the Queen's Windsor Castle home and Balmoral, in Scotland, where she spent her final days.
Portraits of Elizabeth were posted on billboard screens in central London's Piccadilly Circus and the city's Canary Wharf financial district.
Echoes of 'God Save The Queen' rung out.
His Majesty the King, Charles III, paid tribute to his "beloved mother".
"We mourn profoundly the passing of a cherished sovereign and a much-loved mother," he said. "I know her loss will be deeply felt throughout the country, the realms and the Commonwealth, and by countless people around the world."
The new King said his family's mourning would be comforted "by our knowledge of the respect and deep affection in which The Queen was so widely held."
Prince Harry and Meghan Markle's website for their nonprofit organisation Archewell has transformed with a simple tribute.
The website is completely black, with a message stating: "In loving memory of her majesty Queen Elizabeth II 1926-2022".
Newly appointed British Prime Minister Liz Truss met with the Queen on September 6 as is customary to form a new government. It was the monarch's final engagement.
Truss said Queen Elizabeth had been with her nation "through thick and thin".
"She was the very spirit of Great Britain and that spirit will endure," Truss said from outside 10 Downing St, in an emotional television address.
"Our country has grown and flourished under her reign. Britain is the great country it is today because of her."
Opposition leader Peter Dutton said in a statement there had never been "a more dignified monarch, a more dutiful leader, or a more decent human than Her Majesty Queen Elizabeth II".
"An extraordinary life which touched so many has sadly come to an end," he continued.
"The last page has been inked on an exceptional reign."
Governor-General David Hurley said Australians should take inspiration from the Queen's contribution.
"When I reflect on my own memories – she was my Queen for my whole life – I think of Her Majesty's dignity and her compassion. Her dedication and tireless work ethic. And her selflessness and unwavering commitment to the people that she served. To us," he said in a statement.
Across the world, leaders and citizen have paid their own respects to the woman who had been the face of her nation for more than 70 years.
Other Commonwealth leaders, including New Zealand Prime Minister Jacinda Ardern and Canadian Prime Minister Justin Trudeau, shared emotive statements honouring the monarch.
"Over her reign she has come to define notions of service, charity and consistency. Her commitment to her role and to all of us has been without question and has been unwavering," Ardern said.
"She has also demonstrated courage and compassion and humour. A strong memory I will have of her is her laughter. She was extraordinary."
Indian Prime Minister Narendra Modi said she would be remembered as "a stalwart of our times" who had "personified dignity and decency in public life".
Ireland's president, Michael D Higgins, said the late monarch was "a remarkable friend of Ireland".
US President Joe Biden and First Lady Jill Biden released a joint statement, acknowledging the Queen's "steadying presence" and remembering her as a "stateswoman of unmatched dignity".
"We first met the Queen in 1982, travelling to the UK as part of a Senate delegation. And we were honoured that she extended her hospitality to us in June 2021 during our first overseas trip as President and First Lady, where she charmed us with her wit, moved us with her kindness, and generously shared with us her wisdom.
"All told, she met 14 American presidents. She helped Americans commemorate both the anniversary of the founding of Jamestown and the bicentennial of our independence. And she stood in solidarity with the United States during our darkest days after 9/11, when she poignantly reminded us that 'grief is the price we pay for love.'"
Barack and Michelle Obama celebrated a reign "defined by grace, elegance, and a tireless work ethic, defying the odds and expectations placed on women of her generation".
Donald Trump said the monarch's "historic and remarkable reign left a tremendous legacy of peace and prosperity for Great Britain" and George W Bush called her "a woman of great intellect, charm, and wit", saying Americans had always appreciated her "strong and steadfast friendship".
Flowers were laid outside the United Kingdom Consulate General in New York.
In Washington DC, the US flag was lowered to half staff to mark the passing of a monarch whose legacy President Biden said "will loom large in the pages of British history, and in the story of our world".
Her death was also marked in European cities.
In Berlin, flowers and candles were laid outside the UK embassy while in Venice 'God Save the Queen', the British national anthem, was played outside the Italian city's Festival Buildings.
Lights were dimmed across the UK and abroad following the death of the Queen.
Theatres across the UK and landmarks including the Eiffel Tower and London Eye switched off their lights as a mark of respect. In New York, the Empire State Building glowed in regal purple.
- With AAP.
Feature Image: Getty.