A proud Briton waits on Westminster Bridge for the Royal Barge to pass the House of Commons and the Big Ben clocktower during the Thames Diamond Jubilee River Pageant in London

1,000 boats were to sail down the Thames on Sunday in a flotilla tribute to Queen Elizabeth II's 60 years on the throne that organizers are calling the biggest gathering on the river for 350 years.

Despite cool, drizzly weather, hundreds of thousands of people are expected to line the riverbanks in London, feting the British monarch whose longevity has given her the status of the nation's favourite grandmother.

The Queen and members of her family will lead the river pageant aboard a flower-bedecked royal barge, accompanied by skiffs, barges, narrowboats, motor launches, row boats and sailing vessels from around the world.

A proud Briton waits on Westminster Bridge for the Royal Barge to pass the House of Commons and the Big Ben clocktower during the Thames Diamond Jubilee River Pageant in London

The spectacle is a tribute to Britain's past — monarchs used the river as their main highway for centuries, and naval power built the island nation's once-great empire — as well as its abiding love of boats and the sea.

Among the flotilla vessels will be several of the "Dunkirk Little Ships," private boats that rescued thousands of British soldiers from the beaches of France after the German invasion in 1940 — a defeat that became a major victory for wartime morale.

The four-day Diamond Jubilee celebrations also include thousands of street parties across the country on Sunday and a Monday pop concert in front of Buckingham Palace featuring Elton John and Paul McCartney.

The celebration kicked off Saturday with a royal day at the races, as the queen watched a horse with the courtly name of Camelot win the Epsom Derby. Jubilee festivities officially began with a 41-gun salute fired by the King's Troop, Royal Horse Artillery at Horse Guards Parade in central London.