Updated 7.50pm

King Charles III vowed Friday to emulate his late mother's long life of service to Britain and the Commonwealth, and elevated his heir William to become the new prince of Wales, in an emotive televised address.

In his first spoken remarks since ascending the throne upon Queen Elizabeth II's death, Charles also declared his "love" for his estranged younger son Harry and Harry's wife Meghan.

The new monarch further said he could "count on the loving help of my darling wife, Camilla" after she became queen consort.

A special session of the House of Parliament, called to pay tribute to Elizabeth II, was suspended while the monarch made his broadcast.

Charles said he shared the public's "sense of loss beyond measure" after his mother passed away on Thursday aged 96, after a record-breaking reign of 70 years.

"That promise of lifelong service I renew to you all today," he said.

"As the queen herself did with such unswerving devotion, I too now solemnly pledge myself, throughout the remaining time God grants me, to uphold the constitutional principles at the heart of our nation."

Addressing his "darling Mama", joining his father the late Prince Philip, who died last year, "I want simply to say this: thank you", the new king said.

"Thank you for your love and devotion to our family and to the family of nations you have served so diligently all these years. May flights of angels sing thee to thy rest."

As heir to the queen, Charles was duke of Cornwall and duke of Rothesay in Scotland, titles that passed immediately to William on Thursday. 

But the highest title for the heir to the throne, prince of Wales, remained in the monarch's gift to bestow or withhold.

"Today, I am proud to create him prince of Wales, Tywysog Cymru (in Welsh), the country whose title I have been so greatly privileged to bear during so much of my life and duty," Charles said.

"With Catherine beside him, our new prince and princess of Wales will, I know, continue to inspire and lead our national conversations, helping to bring the marginal to the centre ground where vital help can be given."

The date of the queen's state funeral has yet to be confirmed but is expected on September 19.

"In a little over a week's time we will come together as a nation, as a Commonwealth and indeed a global community, to lay my beloved mother to rest," Charles said.

"In our sorrow, let us remember and draw strength from the light of her example," he said.

"On behalf of all my family, I can only offer the most sincere and heartfelt thanks for your condolences and support.

"They mean more to me than I can ever possibly express."

Return to London

Earlier, King Charles III returned to London for the first time since the death on Thursday of of the Queen. 

He got out of his car to meet some of the thousands of people gathered to mourn and greet the new monarch.

He shook hands, accepted flowers and waved as people held up their phones to take selfies, while others offered some words of condolence, and calls of "We love you King Charles" were heard.

"I saw the top of his head, I wasn't expecting to, I was only coming to bring my flowers," said Apophia Othieno, a lecturer, adding: "It was lovely."

There were impromptu renditions of the national anthem, with the word "queen" switched to "king", and cries of "hip, hip hooray".

Charles, 73, wearing a black suit and tie and white shirt, afterwards walked to see some of the bouquets and tributes left at the gates of the palace for his late mother.

Public reactions

"It was impressive, touching, a good move to come out to the crowds," said Ammar Al-Baldawi, a 64-year-old retiree from north of London.

"These are true loyalists here and it's nice to see him back in post, taking charge of the family and the Crown, which is reassuring."

Charles was joined by his wife Camilla, the Queen Consort, before they went inside, where the new king was due to record his inaugural television address to the UK and the Commonwealth.

They had flown down from Scotland where they had been with the queen at her Balmoral estate, where she died on Thursday aged 96 after a record-breaking 70 years on the throne.

"He's got a hard act to follow," said Stephen Johnson, a 56-year-old Londoner.

He said he was feeling "very emotional", similar to when Charles' ex-wife Diana died in a car crash in Paris in 1997.

"I'm still getting my head round King Charles III," he told AFP.

"He's our king now, we've got to love him but memories of Diana are fresh, only last month we marked the 25th anniversary of her passing.