Among the guests are world leaders including US President Biden and hundreds of other foreign dignitaries. Around 200 people recognised in the Queen's birthday honours are also there, BBC reports.

King Charles III led a sombre procession behind his mother's coffin from Westminster Hall to the abbey.

The Queen's coffin was conveyed - in the first of three processions throughout the day - through Parliament Square, a distance of about 820 feet.

The Prince of Wales and the Duke of Sussex walked side-by-side behind their father, the King. The King walked alongside his siblings, the Queen's four children, the report said.

The procession from the abbey saw the State Gun Carriage carry the coffin, drawn by 142 sailors. A guard of honour stood in the square made up of all three military services.

As they walked to the abbey the royals were accompanied by the Massed Pipes and Drums of Scottish and Irish Regiments, the Brigade of Gurkhas and the Royal Air Force and the tolling of the abbey bell.

President Biden, French President Emmanuel Macron and Canadian Prime Minister are among the world leaders who have arrived at the abbey, while six former British prime ministers are also present.

Some 2,000 mourners are bidding farewell to the Queen at the state funeral, including 500 dignitaries - with presidents, prime ministers and foreign royalty among the guests.

As London prepares for as many as one million visitors for the historic occasion, roads and bridges are closed to traffic and an unprecedented security operation is under way.

All public viewing areas for the procession are already full, London's City Hall said.

Millions of people will be watching the funeral across the country and most workplaces are closed for a bank holiday.

(With UNI inputs)