More than 20,000 cars were sold in Beijing in the first week of December as citizens scrambled to buy vehicles ahead of curbs aimed at reducing the city's massive traffic jams, state press said Thursday.

Sales were driven by fears that China's government would restrict purchases by capping the number of car plates issued in the congested capital, the Beijing News reported.

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.

Vehicle sales in the first week of December were more than double the 9,000 cars sold in the same period last year, the paper said.

As of December 5, Beijing had 4.71 million registered cars on its crowded roads, it added.

China outpaced the United States as the world's top auto market in 2009 when 13.64 million units were sold nationwide. That sales figure was already surpassed in the first 10 months of this year.

Relieving traffic jams in Beijing, Shanghai, Guangzhou and Chongqing -- China's biggest cities -- will be a top government priority in the coming years, Xinhua news agency said earlier this week.

According to the China Daily, new car restrictions for Beijing will include an odd-even licence plate restriction system for the city centre, while buyers will have to have a parking permit before they are allowed to purchase cars.

A new two-yuan (0.30-dollar) traffic "congestion fee" will also be charged for every litre (quart) of gasoline or diesel, the paper said.

The capital would also restrict car purchases to those who have Beijing residence permits, while each household would only be allowed one car, it said.

Beijing government officials refused to confirm the content of the new measures, only saying that the traffic management plan had been basically approved by the nation's powerful economic planning agency.