King Charles III greets the public on arrival at Buckingham Palace

New head of state shakes hands with well-wishers after returning from Balmoral where Queen Elizabeth II died

Britain's King Charles III arrives back in London a day after the death of his mother, Queen Elizabeth II. AP

King Charles III greeted his new subjects with handshakes and smiles on Friday as he returned to Buckingham Palace a day after the death of his mother, Queen Elizabeth II.

Britain's new king spoke to well-wishers before walking through the gates of the palace, in a surprise addition to the carefully choreographed 10-day mourning period.

As mourners offered their condolences on the queen's death, and one woman leaned in to kiss him on the cheek, a small group of admirers struck up the tune of the amended national anthem, God Save the King.

The king, who arrived with his wife Camilla, now the queen consort, bowed his head as he inspected the flowers that mourners had left at the palace railings.

The couple were driven to the palace after landing at RAF Northolt, a military airfield in west London, on their return from the Balmoral estate in Scotland where the queen died on Thursday.

King Charles, 73, returned to the palace as sunshine broke out to replace the gloomy skies that had greeted mourners earlier on Friday as they left handwritten tributes and came to witness a moment of history.

While union flags are flying at half-mast during the 10-day mourning period, the royal standard was raised above Buckingham Palace to signal that a new monarch was in residence.

The king was expected to address the nation later on Friday.

Although he assumed the throne at the moment of the queen's death, a formal proclamation ceremony will take place early on Saturday with an Accession Council of senior politicians and functionaries.

As part of the theatre of the occasion, the proclamation will first be read out from a balcony at St James's Palace in London, then at the Royal Exchange in the city's financial centre and subsequently in Scotland, Wales and Northern Ireland.

Bells rang out from Britain's most historic churches on Friday as part of the nationwide tributes to the queen, whose 70-year reign was the longest of the monarchy's 1,000-year history.

The bells of Westminster Abbey, St Paul’s Cathedral, York Minster and those of other church towers tolled to salute the queen at midday.

A 96-gun salute, one for every year of the queen's life, followed an hour later at the Tower of London, Hyde Park, other British landmarks and Royal Navy ships at sea.

St Paul’s will hold a service of prayer and reflection on Friday evening at which Prime Minister Liz Truss is expected to attend and 2,000 members of the public were offered seats on a first-come-first-serve basis.

Ms Truss paid tribute to the queen at the start of a two-day mourning period in Parliament, during which MPs will assemble for a rare Saturday session to pay their respects.

Britain in mourning after Queen Elizabeth's death — in pictures

“She was the rock on which modern Britain was built,” the prime minister said. “She bequeaths a modern, dynamic nation that has grown and flourished under her reign.”

Former prime minister Boris Johnson, one of the last people to see the queen when he formally resigned at Balmoral on Tuesday, said she had appeared “as radiant and knowledgeable and as fascinated by politics as ever”.

“Think what we asked of her … to be the figurehead of our entire system, the keystone in the vast arch of the British state,” Mr Johnson said.

Many sporting events were cancelled out of respect for the queen, including Premier League football fixtures and the second day of a Test match between England and South Africa's cricketers.

The beginning of the new monarch's reign will also bring a host of changes to practical and symbolic parts of life, from the face on coinage and banknotes to the new moniker of “His Majesty's Government”.