A giant clock counting down to the 2012 London Olympics stopped yesterday, less than a day after being started in Trafalgar Square.

The digital clock, which is made by Olympic sponsor Omega, was stuck at 500 days, 7 hours, 6 minutes, 56 seconds.

"We are very disappointed that it has stopped working," Omega said in a statement to The Associated Press. "It's obviously a technical fault and we've got people working on it now."

Omega is part of the Swatch Group AG, the world's largest watchmaker.

Four British Olympic champions — rowers Pete Reed and Andy Hodge and sailors Iain Percy and Andrew Simpson — unveiled the steel clock on Monday amid pyrotechnics beneath Nelson's Column to mark the 500-day countdown to the July 27, 2012 opening ceremony.

"The clock underwent rigorous testing by our experts before the launch," Omega said. "This is very unusual and we are hoping to have it back up and running soon."

London organizing committee chairman Sebastian Coe had said the clock would serve as a "daily and hourly reminder to everyone who visits Trafalgar Square that the countdown to the start of London 2012 has well and truly begun and that the greatest show on earth is soon coming to our country."

The Paralympic countdown on the other side of the clock, which is 8.5 meters (27 feet) high and 5 meters (16 feet) long, is still working.

The clock's failure wasn't the only Olympic glitch on yesterday, when 6.6 million tickets went up on sale. A few hours into the ticket launch, fans with Visa credit cards which expire before the end of August found that London organizers were unable to process their orders.

Visa is an Olympic sponsor and the only card that can be used to purchase tickets.