Huge underground roads are to be built in the Chinese capital, state media said Monday, in the latest effort to relieve the chronic gridlock paralysing Beijing.

Mayor Guo Jinlong told local lawmakers at their annual legislative session that building tunnels in the city centre was a priority for 2011, the China Daily reported.

"The traffic jams result from the growth in the number of automobiles. The situation demands immediate attention," Guo was quoted as saying.

Officials in Beijing are battling dire traffic and air pollution -- both of which are among the world's worst -- and the problems are only getting worse as the city's increasingly wealthy citizens buy more cars.

Last month, the city government announced new restrictions that will only allow 240,000 new passenger cars to hit the road in Beijing next year -- a third of the number registered in 2010.

China has also scrapped a tax cut on small passenger cars put in place as part of a massive stimulus package introduced to fight the global financial crisis.

According to the report, the tunnels will be located on the east and west sides of a ring road around the city centre that is often severely congested.

Zhou Nansen, vice head of the Beijing Municipal Commission of Urban Planning, said these would be "the world's most difficult tunnels to dig" due to a complex underground sewage system and the presence of archeological relics.

The commission was not immediately available for comment when contacted by AFP.

Another two-kilometre (1.2-mile) long tunnel will be built under Wangfujing Avenue, a popular commercial pedestrian street in the city centre, the report said.

Lawmakers also discussed the possibility of doubling the 336-kilometre-long subway network by 2015, and nearly tripling it in length by 2020, as other ways to relieve congestion, it added.