King Charles III crowned at London's Westminster Abbey UPDATED

King Charles III was crowned on May 6 in Britain's biggest ceremonial event for seven decades, a sumptuous display of pageantry dating back 1,000 years.

In front of a congregation of about 100 world leaders and a television audience of millions, the Archbishop of Canterbury, the spiritual leader of the Anglican Church, slowly placed the 360-year-old St Edward's Crown on Charles' head as he sat upon a 14th-century throne in Westminster Abbey, Reuters reports.

The historic and solemn event dates back to the time of the 74-year-old's predecessor William the Conqueror in 1066.

Charles' second wife Camilla, 75, will be crowned queen during the two-hour ceremony, which while rooted in history, is also an attempt to present a forward-looking monarchy, with those involved in the service reflecting a more diverse Britain and leaders from all faiths.

For a nation struggling to find its way in the political maelstrom after its exit from the European Union and maintain its standing in a new world order, its supporters say the royal family provides an international draw, a vital diplomatic tool and a means of staying on the world stage.

After the service, at around 13:00 BST, King Charles and Queen Camilla will travel in the Gold State Coach back to Buckingham Palace, in a spectacular mile-long (1.6km) procession, with 4,000 soldiers and 19 military bands.

The guest list also includes Prince Harry, the Duke of Sussex, who arrived from the United States on May 5 on a commercial flight.

It will be the first time since the release of the duke's memoir that he will have been seen in public with his brother, Prince William, the Prince of Wales.

It is thought Prince Harry may fly back to the US a matter of hours after the ceremony to rejoin his wife Meghan with their son Archie celebrating his birthday the same day.

There has been controversy over whether people at home were being asked to pledge their allegiance to the King.

The Church of England has made clear this is entirely optional and people might instead have a "private moment of reflection".