By Quentin Somerville BBC News, Shanghai

Workers have failed in a third attempt to seal a poisonous leak from a gas well in the remote hills of the Chongqing region of China.

Although there have been no injuries, around 15,000 people have been evacuated from their homes.

In December 2003, a leak from a well in the same area left a total of 243 people dead.

A cloud of toxic gas killed residents in their sleep in one of China's worst industrial accidents.

Homeless

Emergency workers have been unable to bring the gas well under control since it began leaking almost a week ago.

They have been burning off the poisonous gas to prevent it from collecting in the area.

State media reports that local officials have been struggling to raise emergency supplies for those left homeless.

The latest leak was spotted just as a new gas well was being completed.

Gas company workers noticed that a section of the river near the well had started to bubble.