King Charles and the Prince and Princess of Wales have greeted well-wishers during a walkabout outside Buckingham Palace.
Thousands – including those draped in the colours of the Union Jack – have lined the streets on the procession route ahead of Saturday’s Coronation.
King Charles had earlier met with leaders of Commonwealth countries.
Charles and Camilla, the Queen Consort, earlier attended a rehearsal at Westminster Abbey.
The walkabout on The Mall took place under high security, supported by dozens of cars and police on motorbikes.
King Charles shook hands and chatted with members of the public, some of whom said “Best of luck” and “Good luck tomorrow!”
Prince William and Catherine posed for photographs with supporters they met.
Speaking to the PA news agency, one woman called Faby, from London, said she was able to shake hands with the King, and found him “charming”.
“It was incredible,” the 55-year-old said. “It’s not every day you get to shake hands with the King. It was so lovely.”
“It is a moment of celebration, enjoy tomorrow,” Catherine said to one woman.
She appeared to take part in a video call at one stage before also speaking on another person’s phone then handing it back.
As well as Union Jacks, other flags on display included ones representing Germany, Wales, Canada and Australia. Some revellers sang God Save the King, while cries of “Hip, hip, hooray” also rang out.
King Charles had earlier hosted a special lunch at Buckingham Palace for leaders of the Commonwealth realms, the 15 countries (including the UK) where he is monarch.
Attendees included UK Prime Minister Rishi Sunak, Australian Prime Minister Anthony Albanese, and Prime Minister of New Zealand Chris Hipkins.
Saturday’s Coronation begins at 11:00 BST (10:00 GMT) in Westminster Abbey, and will be led by the Archbishop of Canterbury.
At 13:00, the King and Queen will leave Westminster Abbey in a ceremonial procession through London back to Buckingham Palace, joined by other members of the Royal Family.
As part of the Coronation, for the first time the public are being given an active role in the ceremony and will be invited to swear allegiance to the King.
The “homage of the people” is a new addition to the ancient ceremony, which is being led by Justin Welby.
It was revealed, along with other details of the service, in a liturgy published by Lambeth Palace last weekend. Lambeth Palace said the liturgy had been produced “in close consultation” with the King and the government.
Campaign group Republic called the idea “nonsense” and “offensive”.
The King’s close friend and biographer, broadcaster Jonathan Dimbleby, earlier said the King would find the idea of people paying homage to him during his Coronation “abhorrent”.
Scheduled as part of the pageantry on Saturday is a fly-past, but it will be dependent on the weather, with a 70% chance of showers at the same time.
Royal fans who will be in London to celebrate the occasion are advised to bring umbrellas, cagoules and waterproof jackets.
Royal Air Force Air Chief Marshal Sir Michael Wigston said “it’s 50/50” as to whether a fly-past scheduled to go over The Mall and Buckingham Palace after 14:15 BST will happen.
It will consist of more than 60 aircraft from the Royal Navy, British Army and Royal Air Force – including the Red Arrows – but a final decision will be made just one or two hours before it is due to start.
BBC Weather forecaster Chris Fawkes said cloud was expected to “quickly thicken” during the morning with “outbreaks of rain moving in”.
“The rain will often tend to be light and drizzly, but a few heavier bursts are possible,” he said.
“The weather will slowly become drier through the afternoon, perhaps with some sunny spells to end the day.”