A total of 31 people were killed and nine were missing after two lorries carrying dangerous chemicals collided in a Chinese tunnel, triggering a huge explosion, authorities said Thursday.

A methanol leak from the front vehicle started a fire, which caused the blast and ignited other trucks and their loads in the tunnel in Jincheng, in the northern province of Shanxi province, the city government's news office said in a statement.

Previous Chinese media reports had said 12 people died at the scene and another later in hospital after the accident on March 1.

The city government statement, posted on its verified account on Sina Weibo, a Chinese equivalent of Twitter, did not explain how the toll had more than tripled.

More than 200,000 people die on Chinese roads every year, according to reports, with safety and driving standards often ignored.