(AFP) - With a trumpet fanfare and gun salutes, Charles III was officially proclaimed king at a pomp-filled ceremony on Saturday, at which he pledged to emulate his late mother Queen Elizabeth II and serve for the rest of his life.

A court official wearing a feathered bicorn hat declared Charles "our only lawful and rightful" monarch from the balcony of St James's Palace after a historic Accession Council meeting of senior royals, clergy and government.

"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 a speech before swearing an oath.

"In taking up these responsibilities, I shall strive to follow the inspiring example I have been set."

Eight trumpeters accompanied the proclamation which was followed by a rousing three cheers for the new king by red-jacketed Coldstream Guards soldiers, doffing their distinctive bearskin hats.

Ceremonial gun salutes boomed simultaneously across the United Kingdom and the proclamation -- a hangover from the past where the new monarch needed to be announced to their subjects -- was also read publicly in Scotland, Northern Ireland and Wales.

Charles, 73, automatically became monarch upon the queen's death Thursday, but the centuries-old constitutional formality -- broadcast live for the first time -- is the latest step in the setpiece 10-day programme building up to her state funeral.

An emotional Charles set the tone for his reign in a televised address Friday in which he hailed his "darling mama" for her "unswerving devotion" during her record-breaking seven decades on the throne.

"Thank you for your love and devotion to our family and to the family of nations you have served so diligently all these years," he said.

"May flights of angels sing thee to thy rest," he added, quoting Shakespeare's "Hamlet".

The speech dominated the front pages of Britain's newspapers on Saturday, with his heartfelt tribute to his mother headlining the Daily Telegraph, Daily Express, Daily Mail, The Sun, and Daily Star.

Charles looking pensive as he arrived at Buckingham Palace for the first time as king made the front page image on The Independent, The Guardian and The Times, which also carried the words "God Save the King".

The new king also named his elder son and heir Prince William, 40, as the new Prince of Wales, while expressing love for his younger son Harry and daughter-in-law Meghan.

The move means William's wife Kate assumes the Princess of Wales title once held by his mother and Charles' ex-wife, the late Princess Diana.

- Flower, cheers, kisses -

Crowds have massed outside Buckingham Palace both to mourn the queen and to wish Charles well, some of them shouting "God Save the King" as he greeted them on his return from Scotland on Friday.

The oldest monarch to ascend to the British throne, he received flowers, cheers and even kisses after travelling from the Balmoral retreat where his 96-year-old mother passed away peacefully.

Earlier, church bells and ceremonial gun salutes for the departed monarch rang out around the UK as it tries to come to terms with the passing of the only monarch most have ever known.

As Charles's pre-recorded address was broadcast to the nation, dignitaries attended a remembrance service at St Paul's Cathedral which saw the first official rendition of the updated national anthem.

"Suddenly you feel that he's his own person," said Barbara Lewis, a retiree from west London who was among several hundred mourners outside the domed landmark.

Buckingham Palace revealed Charles and other members of the royal family would observe an extended mourning period from now until seven days after her funeral.

The date of the funeral, which will be attended by heads of state and government, has yet to be officially announced but is expected to be on Monday, September 19.

US President Joe Biden has said he will attend. The Kremlin said Russian President Vladimir Putin will not.

The queen's London palace has become a magnet for thousands of mourners, with flowers piling up in one of many poignant signs of the genuine reverence felt for her.

- 'Keep everything going' -

Leading two days of tributes to the queen in parliament, British Prime Minister Liz Truss -- only appointed by the late monarch on Tuesday -- offered the nation's support to Charles as she acknowledged the "awesome responsibility" upon him.

At their first formal audience at Buckingham Palace on Friday, Charles told her his mother's death was "the moment I've been dreading, as I know a lot of people have, but you try and keep everything going".

While the government has said there is no obligation on organisations to suspend business during its 10-day mourning period, many are doing so out of respect.

England's Premier League postponed all matches this weekend, while railway and postal workers halted upcoming strikes over pay amid soaring inflation and spiralling energy prices gripping Britain.

The queen's death comes as the government strives to rush through emergency legislation to tackle the kind of war-fuelled economic privation that marked the start of her reign in 1952.

Elizabeth's public appearances had become rarer in the months since she spent an unscheduled night in hospital in October 2021.

Although smiling, she was visibly thinner and stooped in her last official photographs from Tuesday when she appointed Truss.

The new leader was the 15th prime minister of her reign, which started with Winston Churchill in 1952.

- Lying in state -

Elizabeth's body is expected to remain at Balmoral before being taken to the Palace of Holyroodhouse in Edinburgh on Sunday.

From the Scottish capital, her coffin is due to travel to London on Tuesday to lie in state for several days.

Officials expect more than one million people to file past the catafalque in Westminster Hall, the oldest part of the UK parliament complex, before the televised funeral service at Westminster Abbey opposite.

The funeral will be a public holiday in the form of a Day of National Mourning.

Charles's coronation, an elaborate ritual steeped in tradition and history, will take place in the same historic surroundings, as it has for centuries, on a date to be fixed.

Queen Elizabeth II came to the throne aged just 25 in a blighted post-war world dominated by political figures from Churchill to Mao Zedong and Joseph Stalin.

In the ensuing decades, the last vestiges of Britain's vast empire crumbled, while at home Brexit shook the foundations of her kingdom.

Her family endured a series of scandals and the death of Diana in a car crash in Paris in 1997, which she was initially seen as responding poorly to.

But throughout, she remained consistently popular and was head of state not just of the United Kingdom but 14 former British colonies, including Australia and Canada.

© Agence France-Presse