London (CNN) -- Dragon boats, a floating belfry and the royal barge are among more than 1,000 vessels preparing to transform London's River Thames into a spectacular floating tribute to the 60-year reign of Queen Elizabeth II.
About 20,000 people will take to the water Sunday for a river pageant -- inspired by regal riverside celebrations of the past -- which is set to be the largest such event on the Thames for hundreds of years. The event is set to be a highlight in a four-day weekend of celebrations for the queen's diamond jubilee.
After gathering upriver in west London, the seven-mile long flotilla will wend its majestic way from Battersea Bridge to Tower Bridge, passing through the heart of Britain's capital city over the course of several hours.
At the front will be about 300 man-powered boats, with thousands of volunteers propelling them downriver, flags and streamers fluttering around them. A barge carrying the eight Royal Jubilee Bells -- the largest of which, at nearly half a ton, is named for the monarch -- will lead the way, its peals of bells to be echoed from church towers along the river.
Next will come passenger boats, pleasure boats, historic wooden vessels -- the oldest built in 1740 -- and boats carrying members of the armed forces, police and fire services. One of the boats taking part, the Amazon, also took part in the 1897 Diamond Jubilee celebrations for Queen Victoria, Britain's longest-serving monarch and the only other to reach the landmark 60 years on the throne.
The biggest cheer will no doubt come for the present queen, who will be carried aboard a specially converted royal barge, opulently draped in red and gold.
Huge numbers of flag-waving spectators are expected to line the banks, despite the forecast for rain. Millions more around the world are likely to watch the spectacle unfold on television.
Sailing boats that are too tall to pass under the 14 bridges along the river pageant route will line the river from London Bridge to Wapping, in the east, creating an avenue of sails set against the Tower of London and the city's financial center.
The queen will disembark at Tower Bridge and watch as the remainder of the river pageant passes in a riot of color and noise.
More than 14 miles of bunting in the colors of the Union Flag, or the Union Jack as it is commonly referred to, will be strung along the route, pageant organizers say.
London's Metropolitan Police said as many as 6,000 extra officers would be on patrol during jubilee events. The force will deploy more than 20 police boats during the river pageant, as well as carrying out searches on shore with dogs, and using rope climbing teams to inspect the bridges. Police divers will carry out underwater checks of piers and boats.
The huge security operation comes as London prepares to host the 2012 Olympic Games, which open in late July.
Outside the capital, Britons are expected to gather for thousands of Jubilee-themed street parties and barbecues Sunday. Stores have been filled for weeks with an array of patriotic paraphernalia, from flag-adorned teapots to aprons to picnic sets, to help hosts set the scene for what is billed as a national celebration.
The queen, known for her love of horse racing, kicked off the long weekend at Epsom Downs racecourse Saturday, where she attended the Derby, Britain's most prestigious racing meet, with her husband, the Duke of Edinburgh.
Singer Katherine Jenkins performed the national anthem and the King's Troop Royal Horse Artillery fired a gun salute in the Queen's honor.
The celebrations continue on Monday and Tuesday, which have been declared public holidays to mark the diamond jubilee.
An afternoon garden party at Buckingham Palace will be followed Monday evening by a televised pop concert outside the palace grounds.
At the end of the concert, the queen will take to the stage to light the "National Beacon," which will be on the Mall. She will use a diamond made from crystal glass, which has been on display at the Tower of London from the beginning of May, to light the flame.
More than 4,000 beacons will be then lit in communities throughout the United Kingdom, along with the Commonwealth and UK Overseas Territories.
Tuesday will be a day of pomp and ceremony, as the queen attends a service of thanksgiving at St. Paul's Cathedral, followed after lunch in Westminster by a carriage procession back to Buckingham Palace, where she will appear on the balcony, flanked by members of the royal family.