After Moscow, New York and Madrid were eliminated in the first three rounds, London beat its cross-Channel opponent 54-50 on the fourth ballot of the International Olympic Committee vote - capping the most glamorous and hotly contested bid race in Olympic history.

Londoners celebrate in the city's Trafalgar Square after London was awarded the 2012 Olympic Games yesterday. [AFP]

Paris had been the front-runner throughout the campaign, but London picked up momentum in the late stages with strong support from Prime Minister Tony Blair.

Part of London's pitch was that it stepped in to help the Olympic movement by staging the games as Europe was still recovering from World War II.

The race had been considered too close to call as an unprecedented collection of world leaders and sports celebrities converged on Singapore to lobby for the bids.

London's victory handed Paris a third stinging Olympic defeat in 20 years, following failed bids for the 1992 and 2008 Olympics. Paris hasn't hosted the games since 1924.

IOC President Jacques Rogge opened a sealed envelope and declared the result in a live televised ceremony: "The International Olympic Committee has the honour of announcing that the Games of the 30th Olympiad in 2012 are awarded to the city of London."

The tan-suited London delegates in the convention hall leaped out of their seats, arms raised in jubilation and cheering wildly.

In London, crowds cheered and waved flags as they watched the announcement from Singapore on a giant screen in Trafalgar Square, and in the east London area where the main Olympic complex will be based.

People react after London was awarded the 2012 Olympics, in the Paris townhall, Wednesday July 6, 2005. [AP]

In Paris, a hush fell over a crowd of thousands of Parisians gathered expectantly outside City Hall yesterday as rival London defeated the French capital.

Many looked stunned. Some cupped their faces in their hands; others stood silently watching scenes of jubilation erupting in the British capital from TV screens.

The results of the first three rounds came as no surprise. Moscow was always considered the longhshot, with New York and Madrid outsiders. Moscow went out with 15 votes in the first round, New York dropped out next with 16, then Madrid with 31.

Paris had the perceived advantage of bidding for a third time, as the IOC tends to reward persistence. The French capital also had a ready-to-go Olympic stadium in the Stade de France and embraced the IOC's blueprint for controlling the size and cost of the games.

But not even a personal appearance in Singapore by French President Jacques Chirac could secure victory.

British Prime Minister Tony Blair reacts to the news that London has won the right to host the 2012 Olympics, in Gleneagles, Scotland, July 6, 2005. Supporters of London's bid to host the 2012 Olympic Games reacted with joy and surprise to the capital's shock victory on Wednesday while France struggled to comprehend how Paris had lost. [Reuters]

"The heart of Paris and the heart of France are beating in unison in the hope of becoming Olympic host in 2012," Chirac said during the city's final presentation to the IOC. "You can put your trust and faith in France, you can trust the French, you can trust us."

Blair, who spent two days of lobbying in Singapore before leaving to host the G8 summit in Scotland, spoke in a video message - half of which was delivered in French, one of the IOC's two official languages.

"My promise to you is we will be your very best partners," Blair said. "The entire government are united behind this bid. ... It is the nation's bid." London centred its bid on the massive urban renewal of a dilapidated area of East London. It's the fourth bid from Britain after failed attempts by Birmingham for the 1992 Olympics and Manchester for 1996 and 2000.

London got off to a slow start but made big strides under Sebastian Coe, a two-time Olympic 1,500-meter gold medallist who replaced American businesswoman Barbara Cassani as head of the bid in May 2004.