King Charles III's coronation: The biggest moments of the historic event

Wearing suits, fascinators, military uniforms and medals and religious clothing, guests began filing into Westminster Abbey Saturday over three hours before the start of Charles’ coronation service.

Actress Emma Thompson and singer Lionel Richie, who is performing at Sunday's coronation concert, are among the guests.

Watching the coronation service in-person are over 2,200 invited guests who represent over 200 countries, according to Buckingham Palace.

In addition to royal family members, the assembled guests include heads of state, members of foreign royal families, representatives from charities of which Charles and Camilla are patrons, faith leaders, Nobel Prize winners and members of the Diplomatic Corps.

Just as with royal weddings and funerals, Charles’ coronation is expected to be viewed by millions of people around the world.

Cameras are allowed inside Westminster Abbey, so everyone at home will get a chance to see the biggest moments of the day.

ABC News, "Good Morning America" and ABC News Live will have special coverage of the coronation on Saturday, May 6, from 5 to 10 a.m. ET.

The five hours of special coverage will also be available to stream on ABC News' digital platforms, including ABCNews.com and GoodMorningAmerica.com, mobile apps, social platforms and over-the-top (OTT) services.

ABC News Live will also immediately re-air the five hours of coverage from 10 a.m. to 3 p.m. ET on Saturday, May 6.

Anti-monarchists are expected to stage large-scale protests in London on Saturday, despite warnings from authorities and a controversial new law.

More than a thousand people will be protesting in Trafalgar Square, according to Republic, a London-based campaign group advocating to replace the British monarchy with an elected head of state.

Meanwhile, London's Metropolitan Police Service said it will have more than 11,500 officers on duty Saturday, making it "one of the most significant and largest security operations" that the agency has led.

Under a new law that went into effect this week, protesters who block roads and railways could face up to 12 months behind bars and a fine, and police will be empowered to stop and search protesters suspected of having intent to commit an offense.

The coronation festivities kicked off Friday with a welcome reception for foreign guests hosted by King Charles III at Buckingham Palace.

U.S. First Lady Dr. Jill Biden and Ukrainian first lady Olena Zelenska were both spotted entering the palace for the reception.

Inside the palace, Biden and her granddaughter Finnegan Biden were photographed speaking with Kate, the Princess of Wales.

Charles was photographed in conversation with Zelenska.

Around 100 heads of state and 20 royal families will attend Saturday’s coronation service.

In addition to Charles and Kate, other royals at Friday's reception included Prince William; Princess Anne; and Prince Edward and Sophie, the Duchess of Edinburgh.