Britain's King Charles III on Saturday said he was deeply aware of his great inheritance and duties and heavy responsibilities of sovereignty and pledged to strive to follow the "inspiring example" of his mother, late Queen Elizabeth II.

Charles III was proclaimed Britain's new monarch on Saturday in a historic ceremony of the Accession Council that was televised for the first time in history.

"God save the King" were the words with which those gathered reaffirmed the proclamation made by the clerk of the council.

Charles then made his proclamation speech, which began with the most sorrowful duty to announce the death of Queen Elizabeth II.

Queen Elizabeth II, the UK's longest-serving monarch, died on Thursday at Balmoral Castle in Scotland after reigning for 70 years. She was 96.

Charles said his mother late Queen Elizabeth II gave an example of lifelong love and selfless service and her reign was unequalled in its duration, dedication and devotion.

Announcing the death of his "beloved mother", the new King said the whole world sympathises with him in the irreparable loss we've all suffered".

He said his mother gave an example of lifelong love and of selfless service.

"Even as we grieve, we give thanks for this most faithful life," the 73-year-old King said.

Charles said was "deeply aware of this great inheritance and of the duties and heavy responsibilities of sovereignty" that have now passed to him.

"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," he said.

In this purpose, I know that I shall be upheld by the affection and loyalty of the peoples whose sovereign I have been called upon to be, and that in the discharge of these duties I will be guided by the counsel of their elected parliaments," he added.

Charles said he was profoundly encouraged by the constant support of his 75-year-old wife Camilla, the Queen consort of the United Kingdom.

"I take this opportunity to confirm my willingness and intention to continue the tradition of surrendering the hereditary revenues, including the Crown Estate, to my government for the benefit of all, in return for the Sovereign Grant, which supports my official duties as Head of State and Head of Nation," Charles said.

And in carrying out the heavy task that has been laid upon me, and to which I now dedicate what remains to me of my life, I pray for the guidance and help of Almighty God," he said.