Angry protestors surrounded Westminster Abbey while shouting anti-monarchy slogans as members of the Royal Family' arrived for Commonwealth Day.
The group could be seen holding up yellow placards saying 'Not My King' in front of the 11th-century church.
King Charles is attending the Abbey for a Commonwealth Day service, which is his very first as monarch.
Anti-monarchy organisation Republic said yesterday that they were organising a protest at the site in time for the King's arrival.
In a statement they also outlined their ongoing intention to disrupt the coronation celebrations, which they labelled a "pointless parade".
Speaking for Republic, Graham Smith said: "We are continuing a series of protests against the monarchy in the lead up to the coronation. Charles's pointless parade will cost £50-100m and yet it is entirely unnecessary."
"In light of recent arrests, we're determined to get the message across that it's ok to protest against the royals."
The organised protest saw a number of yellow placards held aloft together to spell 'not my King'. One of the protestors, a white woman, was also seen holding a placard which read 'racist Royal Family'.
Video footage then showed the protestors shouting and blowing whistles as the King and Queen Consort stepped out of the royal car across the road.
It comes after a similar demonstration by Republic in Colchester last week as part of their action in the run-up to the coronation.
Unruly scenes saw one man with a megaphone ask the King to "come and talk to your critics" as he and the Queen Consort exited their car upon a visit to the newly-appointed city.
Another high-profile Republic protest also took place in Milton Keynes back in February, with the monarch heckled as he entered the Church of Christ the Cornerstone for a civic reception.
An entirely separate protest outside Westminster Abbey today was staged by LGBT+ groups, who said 22 of the 56 members of the commonwealth have laws against LGBT+ people.
The King and Queen Consort Camilla are leading the procession for today's Commonwealth Day service, followed by the Prince and Princess of Wales.
Prince Edward, the new Duke of Edinburgh, and his wife Sophie, now the Duchess of Edinburgh, will be next before Princess Anne and Sir Tim Laurence.
However, Prince George, Princess Charlotte and Prince Louis aren't on the list, as today is a school day.
Other members of the Royal Family - including Princesses Beatrice and Eugenie - are also expected to attend but will join the main congregation.
The service will include musical performances from saxophonist Yolanda Brown, West End stars Roshani Abbey and Nuwan Hugh Perera, and the all-female Amalgamation Choir, from Cyprus.
Guests of honour among the 2,000-strong congregation include the Commonwealth secretary-general, the prime minister of Samoa, high commissioners, senior politicians and dignitaries from across the UK and the Commonwealth.
Before the service began, King Charles was given a greeting by members of the Ngati Ranana London Maori Club following a traditional dance.
A Commonwealth flag for peace will be carried in the procession of Commonwealth members' flags to mark 2023 as Commonwealth Year of Peace.
The King inherited the official title of Head of the Commonwealth from his late mother, Queen Elizabeth II.
His succession in the role was confirmed following a Commonwealth Heads of Government Meeting in 2018.
