A gas explosion inside a highway tunnel under construction has killed 42 people and injured 11 others in southwest China's Sichuan province.

The explosion is the latest in a series of deadly industrial mishaps that critics blame on China's rapid economic growth. Two coal mine blasts and a mine flooding in the past five weeks killed nearly 300 people.

The gas explosion happened at 2:00 pm (0600 GMT) Thursday, less than 100 kilometers (62 miles) northwest of Chengdu, at an intersection of a highway being built to link the smaller cities of Dujiangyan and Wenchuan, the State Administration for Work Safety said on its website.

The exact number of casualties remains unclear, officials said.

"We're still trying to determine the exact number of victims. We're still carrying out the rescue work," an official at Sichuan's work safety office told AFP.

Thirty-one bodies were found during an overnight search at the blast site, after 11 bodies were found earlier, bringing the confirmed death toll up to 42, the Xinhua news agency said.

Most of the victims were construction workers, it said.

More than 50 rescuers Friday were searching through the rubble while medical workers had arrived on the scene to treat the injured, officials said.

"We're mainly trying to find other victims and saving the injured now," the official said.

Work safety authorities have launched an investigation into the cause of the accident.

Local authorities were meanwhile blocking access for journalists. There were some 400 police officers posted at the scene, state television CCTV said.

The reports, however, did not give any details on how many people were working at the site at the time of the explosion.

The company constructing the tunnel was the state-owned China Railway Engineering Company's branch in Sichuan, Xinhua said.

Construction of roads in China is rapid as the government considers good roads an important contributor to strong economic growth.

China built 352,000 kilometers (218,000 miles) of roads in rural areas in the past two years, more than that built since the Communist Party began ruling the nation more than half a century ago.

Labour and human rights critics argue safety standards are not keeping up with production in China with more than 100,000 people killed in workplace accidents each year, government statistics say.

And a lack of free trade unions also leaves workers little power to demand change, they say.

Two years ago Friday, China's worst industrial accident in recent memory occurred, with an explosion at the Chuandongbei gas field in the southwest Chongqing municipality that killed 243 people and poisoned more than 9,000 others.

PHOTO CAPTION

A survivor of a coal mine blast receives medical attention at a hospital after an explosion in Tangshan, China's Hebei province December 8, 2005. (REUTERS)

Source: AFP