King Charles III is expected to address the nation for the first time as sovereign at 18:00 BST, following the death of Queen Elizabeth II.
Britain’s longest-reigning monarch died peacefully, surrounded by her family, at Balmoral in Scotland on Thursday.
The King has arrived in London, where he is also due to meet Prime Minister Liz Truss later.
Gun salutes are being fired and church bells have tolled as the UK pays tribute to her reign.
As MPs gathered to pay tributes to the Queen, Ms Truss described her as “one of the greatest leaders the world has ever known”.
Labour leader Sir Keir Starmer said her death “robs our country of its stillest point, its greatest comfort, at precisely a time when we need those things most”.
Former PM Boris Johnson, who met the Queen at Balmoral on Tuesday to stand down, described the Queen as “Elizabeth the Great”, adding she had “worked so hard for the good of her country, not just now but for generations to come”.
Charles will be officially proclaimed King at the Accession Council at 10:00 BST on Saturday in a ceremony televised for the first time.
It will be attended by his son the Duke of Cornwall and Cambridge on Saturday, Buckingham Palace said.
The council is also attended by invited Privy Councillors and current serving government ministers – but that could also include former ministers and prime ministers.
After the meeting, the Principal Proclamation, announcing Charles as sovereign, will be read at 11:00 BST from the balcony overlooking Friary Court at St James’s Palace, central London.
