Fears over disruptions to Europe's busiest and oldest transport system overshadowed preparations for the Games as millions of spectators from around the world were due to descend on the British capital.

After London trains ground to a halt on the Central Line during the morning rush hour, an army of Olympic volunteers stepped in quickly to guide crowds of commuters and Olympic fans and staff and the atmosphere was calm and orderly, Reuters reporters said.

London's commuters, accustomed to almost daily delays on the Tube, the world's oldest urban underground, appeared understanding.

"(It's) not too bad actually. They gave us tickets for the bus or train," said Sammy Proctor, 17.

Foreign visitors were also patient, if a bit bemused.

"Getting around has been incredibly easy," said Alexei Kazakov from Russia's Siberia region, who was wearing the full Russian Olympic outfit at the London Bridge railway station.

"There are people everywhere telling you where to go. It's almost as good as the Moscow metro," he added.

The Central Line, which runs east-west across London, was halted after a driver reported smelling smoke just east of Stratford station, the main hub for visitors to Olympic Park, said operator Transport for London.

Part of the line remained shut for about three hours.

To boost commuters' morale, Network Rail, which operates Britain's overground rail infrastructure, has hired a troupe of actors dressed as American tourists from the 1950s in chequered suits and white tasselled cowboy boots, to entertain passers-by.

"We are here to lighten the mood and raise a smile," said Raylene, sporting a blonde beehive wig, as others moved through the station giving high-fives and posing for photos.

London's transport bosses expect an extra 3 million journeys per day during the Games on top of the usual 12 million who use a transport network including the underground, which opened in 1863 during the reign of Queen Victoria.

On Monday, the much criticised system passed its first major test after carrying a million spectators and London's usually sceptical commuters seemed impressed with the handling of Tuesday's outage.

"It's been brilliant, might have been a trial run," said John Rees, 55, from the university town of Cambridge. "Very good organisation." (Additional reporting by Tim Castle; writing by Maria Golovnina; editing by Jason Neely)

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