Elizabeth, who died aged 96 in September last year, was at the castle on the day of the incident, along with her son Charles, now the king, and other close family members.

Elizabeth died aged 96 on Sept 8 at Balmoral Castle leading to 10 days of national mourning and condolences and tributes from across the world for her record-breaking 70-year reign.

Huge crowds thronged the streets of London and at Windsor Castle to witness the moving, grand processions and ceremonies.

The royals followed the coffin up the aisle, with close-up television shots showing the grief on their faces.

In scenes of inimitable pageantry, pall bearers carried her flag-draped casket along the aisle in the country's first state funeral since 1965, when Winston Churchill was afforded the honour.

Among the 2,000 in the congregation will be some 500 world leaders, including Biden, Emperor Naruhito of Japan, Chinese Vice President Wang Qishan, and South African President Cyril Ramaphosa.

World leaders will gather for the funeral for Elizabeth, queen for 70 years whose global stature was almost without equal.

Guns fired every minute at Hyde Park, while parliament's famous Big Ben bell also rang at 60-second intervals.

At the palace, the flag-draped coffin was met by Charles and all the queen's children, grandchildren and their spouses who had gathered together for the first time since their matriarch died.

The death of Britain's longest-reigning monarch has prompted hundreds of thousands of people to gather at royal palaces across the country to express their condolences.

Hundreds of thousands of people are expected to file past her coffin in a round-the-clock lying-in-state on the day of her funeral.

Mourners, some weeping, and others with heads bowed or curtsying, walked slowly past the coffin after having waited patiently for hours to be allowed into the cathedral.