London's Olympic bid team has unveiled a clock in Trafalgar Square which will count down to the announcement of which city will host the Games in 2012.
The clock will countdown to 6 July, when the host city is announced
There are 75 days to go until the International Olympic Committee (IOC) makes its decision.
London is up against Paris, New York, Moscow and Madrid for the chance to stage the sporting event.
The unveiling of the clock, which will count down hours and minutes until 6 July, took place on Friday afternoon.
London 2012 Ambassador Cherie Blair and London 2012 Chairman Sebastian Coe made the unveiling.
'Mad about sport'
"The London 2012 Countdown Clock provides a visual focus for our campaign as we enter the final stages of our bid to bring the Olympic Games to London," said Sebastian Coe.
Secretary of State for Culture, Media and Sport Tessa Jowell, Conservative Shadow Sports Spokesman Hugh Robertson and Liberal Democrat Spokesman for London Sarah Teather also attended.
Cherie Blair, the wife of Prime Minister Tony Blair, said: "London's bid is really being taken seriously.
"London is mad about sport, the UK is mad about sport and all of us here are united in our passion to bring the Olympics and Paralympics to this great country."
Also present were London 2012 Ambassador and 800m runner Jo Fenn, and 2012 Olympic medal hopeful Montell Douglas.
The IOC will announce its decision in Singapore.