International Olympic chief Jacques Rogge gave London a resounding vote of confidence here Wednesday as the one-year countdown to the greatest sporting show on earth got under way.
A day of festivities to mark the milestone culminated with International Olympic Committee (IOC) President Rogge inviting the world's athletes to the 2012 games at a ceremony in Trafalgar Square.
"According to tradition, I invite the participants of the Games to compete in the 30th Olympiad in London. Good luck London," said Rogge, shortly before the crowd counted down to the one-year mark on a giant digital clock.
The ceremony also saw Princess Anne unveil the designs for the medals which some 10,500 athletes from 202 countries will compete for at next year's Games.
An awestruck Rogge had earlier given London's new Aquatics Centre - one of several venues which have been built at the 2.5 square kilometre (one square mile) Olympic Park site in east London - a glowing appraisal.
"I entered the upper deck and I had a visual shock," Rogge said after touring the venue. "I've seen so many venues in my life but never something like this.
"It's absolutely fabulous. The athletics stadium, the Velodrome, the Aquatics Centre, this is really state of the art and a great job done by London."
"It gives me a lot of confidence for the future. I believe the London Games will be a great success.
British diver Tom Daley later christened the diving pool at the Aquatics Centre with a leap from the 10-metre platform.
"It was great," Daley said. "It was a little bit cold. But to think what it's going to be like next year ... it's going to be awesome."
Wednesday also provided an opportunity for London to showcase venues being incorporated into the city's most famous landmarks, including a beach volleyball arena at Horseguard's Parade where tonnes of sand have been deposited.
London 2012 organising committee (LOCOG) chairman Sebastian Coe meanwhile said preparations were on schedule with 90 percent of venues complete, hailing the milestone as a "massive moment in an Olympic city."
"This is an extraordinary day," he said.
Mayor of London Boris Johnson also ratcheted up the hyperbole, saying the city was 12 months away from the "greatest party the planet has ever seen."
British Prime Minister David Cameron said the 2012 Games had "the makings of a great British success story."
"I believe this can be a great advertisement for our country," Cameron said. "We must offer the greatest ever games in the world's greatest country."
London also received applause from Australian Olympic Committee president John Coates, who said next year's Olympics may even surpass the 2000 Sydney Games - widely regarded as the best ever.
"I think we're all pretty proud of Sydney (2000) and many people say that Sydney remains the benchmark," Coates said.
"But from where I've been sitting London has been six months to a year ahead of us in their preparations all the way through since they were awarded the Games six years ago."
" ... these Games now have the very British stamp to them and I think there's every prospect of them surpassing our Games."
While construction work for the Games has progressed smoothly, organisers have come under fire over the distribution for tickets, which saw hundreds of thousands of applicants end up empty-handed.
Coe insists however that the disappointment was unavoidable given the "unprecedented" demand, with around 23 million applications for tickets made by some two million people.
Coe meanwhile said the security plan for the Games was constantly reviewed when asked if last Friday's massacre in Norway had prompted a rethink.
"Security is permanently under review," Coe said. "We never maintain a running commentary but we do have the right teams in the right places.
"We'll do whatever we need to do to make sure the Games are as safe and secure as possible."