London's Tube disrupted

London - Signal failures caused severe delays on a key London Underground line connecting the city centre with the Olympic Park, transport chiefs said Friday, on the first day of athletics at the Games.

The Central Line was partly suspended in east London - home to the Olympic Stadium - for more than an hour at the height of the morning rush hour, on what is is expected to be the busiest day so far.

Severe delays continued across the whole the line, which runs east to west across London and is one of the busiest on the network.

Spectators are heading to the 80 000-capacity Olympic Park stadium for the first track and field events.

Transport for London (TfL), the authority that runs the Underground, said the problems were caused by a failure in its signalling system.

"The suspension has been lifted," a TfL spokesperson said. "We had a good service on all other lines and we were able to get spectators to the Olympic Park in good time for Friday's events."

The high-speed Javelin train connecting the Olympic Park with central London was packed with spectators trying to get around the Central line delays.

The first track and field medals go up for grabs on Friday, while American swimming superstar Michael Phelps is chasing his third gold of the Games.