Authorities in Beijing said Thursday they would slash the number of new cars hitting the city's streets in 2011 as they try to ease the Chinese capital's massive traffic jams.

The city will allow 240,000 passenger cars to be registered next year through a licence plate lottery system, city government officials said.

The figure is about a third of the number of new cars registered in the capital this year. The new rules take effect on Friday and nearly 90 percent of the new licence plates will be allocated for residents.

But authorities admitted that the registration cap along with other measures such as higher parking fees in the city centre and stricter enforcement of traffic rules would not automatically ease the chronic gridlock.

"It will be difficult to dramatically improve the traffic situation in a short time," said Li Shaoming, deputy director of the Beijing Traffic Management Bureau.

"But it can slow down the pace of worsening traffic congestion."

Expectations that the government was going to restrict the number of new number plates issued next year sparked a surge in sales this month, with more than 20,000 cars sold in the first week of December, state media said.

That was more than double the 9,000 cars sold in the same period last year.

Beijing's air is among the most polluted in the world and the problem is getting worse amid high demand for private vehicles from its increasingly affluent residents.

The number of registered cars in Beijing stood at 4.8 million on Thursday, with 750,000 new cars hitting the streets this year -- an average of 2,000 every day -- officials said.

Authorities said the lottery system had been approved by experts to ensure it was fair and transparent.

Other measures announced will require drivers of cars registered outside Beijing to obtain a permit before they can enter the city centre.

Government departments will also not be allowed to increase the size of their fleets for the next five years.

If the current pace of growth in new cars were to be maintained, the city would have seven million by 2015 on a road network that can handle 6.7 million, state media said.

But the current traffic congestion is already so severe that parts of the the city often resemble parking lots.

On a single evening in September, a record 140 traffic jams were observed as the number of vehicles on Beijing's streets exceeded 4.5 million.

The record bottlenecks were worsened by rain and the approach of two national holidays.

China's auto sales are likely to reach 18 million units this year, up 32 percent from 2009 when the nation took the title of the world's top auto market from the United States.