King Charles pledged to follow the example of his late mother as he was officially proclaimed Britain's new monarch today in a historic ceremony featuring pageantry, centuries-old tradition, and cries of "God Save the King".

The death of 96-year-old Queen Elizabeth on Thursday after 70 years on the throne set in train long-established and highly choreographed plans for days of national mourning and a state funeral that will be held in just over a week.

Charles, 73, immediately succeeded his mother but an Accession Council met at St James's - the most senior royal palace in the United Kingdom which was built by order of Henry VIII in the 1530s - today to proclaim him as king.

The council - formed of Privy Counsellors whose centuries-old role has been to advise the monarch - included his son and heir William, wife Camilla and Britain's new prime minister, Liz Truss, who signed the proclamation of his accession.

Six former prime ministers, senior bishops and a swathe of politicians cried out "God Save The King" as the announcement was approved.

"I am deeply aware of this great inheritance and of the duties and heavy responsibilities of Sovereignty which have now passed to me," Charles said.

"In taking up these responsibilities, I shall strive to follow the inspiring example I have been set in upholding constitutional government and to seek the peace, harmony and prosperity of the peoples of these islands and of the Commonwealth realms and territories throughout the world."

Later, on the Proclamation Gallery, a balcony above Friary Court of St James's Palace, the Garter King of Arms, David White, accompanied by others in gold and red heraldic outfits read out the Principal Proclamation, as trumpeters sounded.

"Whereas it has pleased almighty God to call to his mercy, our late sovereign lady, Queen Elizabeth the Second of blessed and glorious memory, by whose decease the crown of the United Kingdom of Great Britain and Northern Ireland, is solely and rightfully come to the Prince Charles Philip Arthur George," White proclaimed.

Soldiers in traditional scarlet uniforms shouted "hip, hip, hurrah" as White called for three cheers for the king.

Watching on were a few hundred people allowed into the court, including small children on parents' shoulders, a woman clutching flowers and elderly people on mobility scooters. Many capture the moment on their smartphones.

Royal pomp

Charles is the 41st monarch in a line that traces its origins to the Norman King William the Conqueror who captured the English throne in 1066. Saturday's events reflected proclamations announcing new kings and queens that date back hundreds of years.

It was the first proclamation of a monarch to be televised. And for most Britons, it was the first such event in their lifetime as Elizabeth was the only monarch they have ever known. Charles himself was just three when she became queen in 1952.

Following the events at St James's, a military band led soldiers, heralds and men in a ceremonial dress carrying standards and pikes, through the ancient City of London to the Royal Exchange, the capital's first purpose-built trading centre that dates back to 1566, where the proclamation was read again.

The announcement was also set to be delivered in other capital cities of the United Kingdom - Edinburgh in Scotland, Belfast in Northern Ireland, and Cardiff in Wales.

The death of Elizabeth, Britain's longest-reigning monarch, has prompted an outpouring of tributes around the globe. Buildings and landmarks in Europe, America and Africa have been lit up in the red, white and blue of the United Kingdom.

In Parliament, lawmakers lined up to swear oaths of allegiance to the new king, led by the Speaker of the House of Commons, Lindsay Hoyle, and Truss was one of the first.

"I swear by Almighty God, that I will be faithful and bear true allegiance to His Majesty King Charles, his heirs and successors according to law, so help me God," the oath said.

People started gathering again today outside royal palaces, with thousands flocking to Buckingham Palace to pay respects to the queen and Charles. Outside the remote Scottish castle, Balmoral, deep in the Scottish highlands, a queue of people waiting to drop flowers ran for more than 500 metres.

"It's a poignant time in our country's history," design manager Ian Bilboe, 54, said. "(We're) here to be part of that and show respect to the late queen and also to the new king."

Charles is king and head of state not only of the United Kingdom but of 14 other realms including Australia, Canada, Jamaica, New Zealand and Papua New Guinea.

'Nation’s grandmother’

Britain has declared a period of mourning until the state funeral for Elizabeth, once described by her grandson Harry as "the nation's grandmother".

The date for that has not been announced but it is expected in a little over a week's time, and Charles announced today that it would be a public holiday.

Leaders from around the world are expected in London for the funeral, including US President Joe Biden, who said on Friday he would attend.

Charles' coronation as king will take place at a later date - and the timing for that is not yet clear. There was a 16-month gap between Elizabeth becoming queen and her coronation in 1953.

The new king vowed on Friday to serve the nation with "loyalty, respect and love" in his first televised address to the nation as king.

Earlier on Friday, returning to London from Scotland where his mother died, he was greeted with cheers, applause and a crowd singing "God Save The King" as he made his first public appearance outside Buckingham Palace.

Charles also said in his address that he had made his eldest son William, 40, the new Prince of Wales, the title that had been his for more than 50 years and is traditionally held by the heir to the throne.

William's wife Kate becomes Princess of Wales, a role last held by the late Princess Diana.

Debate on the monarchy?

Elizabeth, who was 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.

Over the decades she witnessed a seismic change in the social, political and economic structure of her nation. She won praise for guiding the monarchy into the 21st Century and modernising it in the process, despite intense media scrutiny and the often highly public travails of her family.

Charles, who opinion polls indicate is less popular than his mother, now has the task of securing the institution's future.

"While we recognise that many people are reflecting on the loss of the queen, Britain does need a debate on the future of the monarchy in light of King Charles’s accession to the throne," Graham Smith, head of the anti-monarchy Republic group, said.

During Elizabeth's long reign, republican rumblings surfaced on occasion, but the affection and respect she enjoyed meant there was never any serious threat to the monarchy. Now republicans hope the end of the 1,000-year-old institution could be a step closer.

- Reuters