BALMORAL, Scotland: Britain's King Charles will address a nation in mourning on Friday following the death of his mother and the country's figurehead, Queen Elizabeth, at the age of 96.

Charles, who raced to be by the side of the queen before she passed away at her Scottish home on Thursday, was due to travel back to London with his wife Camilla, now Queen Consort, before meeting the prime minister and making a televised statement.

The death of the queen, Britain's longest-reigning monarch and a towering presence on the world stage for seven decades, has drawn condolences from around the world.

At first light in London, members of the public continued laying flower outside Buckingham Palace and billboards across the city displayed messages of condolence. Newspapers ran front-page photo tributes to the queen.

On Thursday, thousands had gathered outside the queen's palace, where the news was met with a stunned silence as the flag was lowered to half-mast.

Many described a sense of shock at the death of the only monarch most Britons have ever known.

"She's the person we've always looked up to," a tearful retiree Christine West told Reuters outside the queen's Windsor Castle home to the west of London. "It's a sad day for us all".

Charles, who automatically became monarch of the United Kingdom and the head of state of 14 other realms, including Australia, Canada and New Zealand, said the death was a moment of great sadness for himself and his family.

"We mourn profoundly the passing of a cherished Sovereign and a much-loved mother. I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world," the 73-year-old said in a statement.

He is expected to meet Prime Minister Liz Truss on Friday before later addressing the country. There will also be gun salutes.

News that the queen's health was deteriorating emerged shortly after midday on Thursday when her doctors said in a statement that she was under medical supervision, prompting her family to rush to Scotland.

The queen had been suffering from what Buckingham Palace had called "episodic mobility problems" since the end of last year, forcing her to withdraw from nearly all her public engagements. Her husband of 73 years, Prince Philip, died in 2021.

Her last public duty came only on Tuesday, when she appointed Truss prime minister - the 15th of her reign.

"The death of Her Majesty the Queen is a huge shock to the nation and to the world," Truss said outside her Downing Street office where the flag, like those at royal palaces and government buildings across Britain, were lowered.

"Through thick and thin, Queen Elizabeth II provided us with the stability and the strength that we needed. She was the very spirit of Great Britain – and that spirit will endure."

SEVEN DECADE REIGN

The news stunned not only people in Britain, with condolences pouring in from leaders around the world.

"Her legacy will loom large in the pages of British history, and in the story of our world," U.S. President Joe Biden said in a statement.

Queen Elizabeth II, who was also the world's oldest and longest-serving head of state, came to the throne following the death of her father King George VI on Feb. 6, 1952, when she was just 25.

She was crowned in June the following year. The first televised coronation was a foretaste of a new world in which the lives of the royals were to become increasingly scrutinised by the media.

"I have in sincerity pledged myself to your service, as so many of you are pledged to mine. Throughout all my life and with all my heart I shall strive to be worthy of your trust," she said in a speech to her subjects on her coronation day.

Elizabeth became monarch at a time when Britain still retained much of its old empire with Winston Churchill her Britain's prime minister, while Josef Stalin led the Soviet Union and the Korean War was raging.

Bereft of its symbol of continuity and resilience, Britain begins its new era in grave economic crisis, marked by ructions with Europe and a populace disaffected by years of political strife and scandal.