Workers in southwestern China are seeking ways to cap a gas well that blew out Tuesday, releasing poisonous fumes that have killed at least 191 people.

Rescue workers coming out of the scene near the southwestern city of Chongqing told state news media that the blast had created a death zone of poison gas spanning several kilometers.

The official news agency, Xinhua, said many of the victims were children, who died after breathing the fumes while sleeping.

An official at the Chongqing government information bureau, who declined to give his name, says crews continued to canvass the area on Friday, looking for further victims. He says health and fire officials remain at the scene as rescue efforts continue.

Xinhua reported without detail Friday that officials were seeking ways to cap the well.

Meanwhile, hospitals worked to treat hundreds of people suffering from chemical burns and poisoning. The government said about 41,000 people had been evacuated within a five-kilometer radius of the blowout.

The news agency said the blow-out happened Tuesday at a gas well that was being dug on a mountainside, in a remote area of Kaixian county. The incident was first reported on Wednesday, when officials said eight people had died.

The death toll mounted quickly Thursday, as rescue workers made their way up muddy mountain roads to the remote villages, where many of the victims were discovered.

President Hu Jintao urged rescue workers to spare no efforts in finding victims and preventing further deaths.

It was not clear what caused the well to burst. Officials said an investigation was underway.

The disaster happened despite recent government efforts to curb the number of workplace deaths in China. In October, officials reported more than 11,000 people had died at work in the first 10 months of the year.