Giant Olympic rings floated down the River Thames to mark 150 days before London 2012.
The 11-metre high rings were attached to a barge and taken on a trip down the river from London Bridge, before being put into storage until the games begin. They will then be launched onto the river again.
The rings, which are coloured on one side and have white LED lights on the other, cost more than £930,000. Another set is already being displayed at St Pancras station and a third set will be suspended from Tower Bridge.
Mayor Boris Johnson also announced free events for every borough during the Games, including a floating opera inspired by The Owl And The Pussycat, which will be staged on the city’s canals. The English National Ballet will also present Like a Fish Out of Water at three London lidos, in Uxbridge, Hampton and Brockwell.
Ruth Mackenzie, director of the London 2012 Festival, said: “London and the UK’s creative industries are world-beating and the London 2012 Festival will show them off to the world.
“With millions of free tickets and opportunities to take part, Londoners and tourists will truly have a summer like no other, thanks to the partnership between the mayor’s office and London 2012 Festival.”
The Queen has appeared outside Buckingham Palace to make an official announcement that she will open the Games. She also unveiled a plaque to mark the 60km walking and cycling Jubilee Greenway route that connects the Palace with the Olympic Park and other main venues.
London 2012 chairman Lord Coe said: “This summer we will be hosting the largest Paralympic Games ever and the opening ceremony on August 29 will be a fantastic event to start us off. The Paralympic Games will undoubtedly be a time of extraordinary pride for our nation, and it is fitting that Her Majesty will declare us under way.”