King Charles has surprised well-wishers outside Buckingham Palace a day before the monarch’s formal coronation ceremony.

A huge security operation is underway in London ahead of this weekend’s May 6 event, as foreign royals and world leaders gather in the country.

But that hasn’t stopped the British royal family greeting fans on the street.

The King left the palace gates in his royal car before stopping halfway down the Mall, where fans are camped out.

He was joined by son William and daughter-in-law Kate who chatted and posed for selfies with members of the public.

Shaking hands with smiling spectators, the King was met with cheers of “hip, hip, hooray!” and “God save the King!” along the grand avenue leading to the palace, which will be a central part of a procession route on Saturday.

“No school?” Charles joked to one child in the crowd who shook the King’s hand.

“You’ve done very well.”

King Charles jokes with royal fans who are camped outside Buckingham Palace. Photo: Getty

One military veteran saluted Charles while others told the King where they had come from: the Netherlands, Poland, the Gambia and Pakistan were among the variety of nationalities represented in the crowd.

King Charles, 74, and his wife Camilla will be crowned at London’s Westminster Abbey in a glittering but solemn religious ceremony with traditions dating back 1000 years, followed by a procession, resplendent with pomp and pageantry.

Earlier, the King met leaders from the Commonwealth, the voluntary associations of 56 countries which he also heads, and held a lunch for prime ministers and royal representatives from the 14 other realms where he is head of state, including Australia and Canada.

Crown Princess Mary of Denmark and Crown Prince Frederik of Denmark at the royal reception. Photo: Getty

Charles automatically became king when his mother Queen Elizabeth died aged 96 in September.

The coronation, although not essential, is regarded as a hugely symbolic moment that legitimises the monarch in a public way.

Across the United Kingdom, preparations are underway for the first coronation since 1953 when Queen Elizabeth was crowned.

The King has even voiced announcements for the London underground network, using the traditional “mind the gap” warning to be cautious on getting on and off the tube trains.

PM meets Commonwealth leaders

Prime Minister Anthony Albanese lunched with other Commonwealth heads of government at Buckingham Palace ahead of the coronation.

Mr Albanese had earlier on Friday met United Kingdom Prime Minister Rishi Sunak for talks he said focused on the AUKUS pact, trade and combating climate change.

Mr Albanese told reporters after the 30-minute meeting in Downing Street that he was glad the UK-Australian free trade deal had been completed in time for the King’s coronation, which he called a “historic event of enormous significance”.

Mr Albanese announced on Thursday that the trade agreement would come into force on May 31.

The PA news agency reported that the Princess of Wales, one of several royals at the lunch on Friday, was seen speaking with Mr Albanese and New Zealand Prime Minister Chris Hipkins.