King Charles III coronation recap: The biggest moments

London's Metropolitan Police Service announced via Twitter that its officers "have made a number of arrests in the area of Carlton House Terrace," which is just west of Trafalgar Square.

"The individuals have been held on suspicion of breaching the peace," police added.

Earlier, officers also arrested four people in the area of St. Martin's Lane, which is just north of Trafalgar Square.

"They were held on suspicion of conspiracy to cause public nuisance," police said. "We seized lock-on devices."

An additional three people were arrested in the area of Wellington Arch, which is situated between the corners of Hyde Park and Green Park, just west of Buckingham Palace.

"They were held on suspicion of possessing articles to cause criminal damage," police said.

Hundreds of anti-monarchy protesters are gathered in Trafalgar Square.

Dr. Jill Biden has arrived at Westminster Abbey to represent the United States at the coronation. She traveled to the U.K. with her granddaughter, Finnegan Biden, who is also attending the coronation.

The first lady, dressed in blue, is seated next to Ukrainian first lady Olena Zelenska. The two first ladies also saw each other Friday night at a reception at Buckingham Palace, where they posed for a photo with Kate, the Princess of Wales.

Around 100 heads of state and 20 royal families are attending today’s coronation.

The world leaders were welcomed Friday night at a private reception at Buckingham Palace.

Hundreds of anti-monarchy protesters have gathered in central London’s Trafalgar Square, just a mile away from Westminster Abbey where Charles will be crowned.

Their chants of "not my king" were met with boos from others in the crowd who are fans of the royals.

-ABC News' Ibtissem Guenfoud and Patrick Reevell

Charles’ coronation is the first since 1953, when his mother was crowned.

The queen’s coronation also took place at Westminster Abbey, where every coronation service has taken place since 1066.

Over 8,000 guests filled the abbey for Elizabeth's coronation, including Charles, who was 4 at the time.

One famous photo shows Charles resting his head on his hand as he stands between his grandmother, Queen Elizabeth The Queen Mother, and his aunt, Princess Margaret.