Beijing, China - One of Beijing's most important subway lines seized up on Monday when the mass of passengers forced workers to close off entrances for safety on the first working day of pre-Olympic traffic restrictions.

Passengers were being allowed off Line 2, which runs in a loop around central Beijing, but not on to it. At least one major transfer station, at Jianguomen, was closed.

'There is a big crush of passengers. We've had to close the line for safety reasons,' said a subway worker, standing in front of locked gates at the Fuxingmen station, a transfer point for Line 1.

Monday marked the first working day of emergency traffic curbs that aim to take half of all cars off the road by utilising an odd-even number plate system. Streets were noticeably quieter, but still busy during the morning rush hour.

Under the new rules, which began on Sunday, cars are banned on alternate days depending on their licence plate number and most official cars have been impounded. Only taxis, buses and Olympic vehicles are exempt.

The government hopes to take around 60 per cent of the city's 3.3 million cars off the roads, the official Xinhua agency reported, and reduce emissions by two-thirds over the two months until the end of the Paralympic Games in mid-September.

The city's chronic pollution has been one of the biggest headaches for Beijing Olympic Games organisers, who are banking on the car bans and last minute factory closures to bring blue skies and easy breathing for athletes.

Three new subway lines opened over the weekend, including an express link to the airport, to help take up the burden from the traffic controls. -- REUTERS