LONDON - Olympic spectators crammed into trains and formed long queues at London train stations on Friday on what is expected to be the busiest day for London's creaking transport system as track and field competitions begin at the main Olympic stadium.

Europe's oldest public transport network has so far coped well with the influx of Olympic fans but the start of the hugely popular athletics events - all taking place at the new stadium in London's Stratford district - could pose new challenges.

Almost a quarter of a million people are expected to descend on the area on Friday. The Olympic Stadium alone has a capacity of 80,000.

Transport authorities called on Londoners to use alternative routes after the Central Line - a major link between the city centre and the Olympic Park - was partly suspended for an hour due to a technical problem.

"During the suspension we advised spectators going to Stratford to use the wide range of other lines serving the Olympic Park," said a London transport authority spokesman.

At King's Cross station, one of London's biggest hubs, there were queues of up to 100 metres (yards) for the high-speed Javelin train service, designed to whisk fans to the Olympic Park in a few minutes.

Fans of all ages with flags of various nations draped around their shoulders waited patiently while Games volunteers in purple uniforms directed the crowds.

London's transport bosses expect an extra 3 million journeys per day during the Games on top of the usual weekday total of 12 million on a transport network that dates, in part, back to 1863.