Authorities evacuated up to 16,000 people, most of them farmers, after the government ordered everyone cleared from within five km (three miles) of the Tuesday disaster in Kaixian county, in the densely populated Chongqing municipality, an oil official said.

"We're very busy. There are patients everywhere. We haven't counted the casualties," said a Kaixian hospital worker.

Some of the victims, who included men, women, children and gas field workers, had been poisoned and others had suffered chemical burns, hospital workers said.

China has a notoriously poor work safety record. More than 95,600 people were killed in work-related accidents in the first nine months of the year.

The cause of the latest disaster was still being investigated but one oil industry official in Chongqing said the well had burst while it was being drilled.

The Xinhua news agency said at least 191 people had been confirmed dead by last evening.

"Chinese leaders called for unreserved efforts in searching and rescuing victims," the official news agency said on its Web site.

Rescue workers carrying oxygen tanks on their backs and wearing masks were seen near the site, said one official.

The private www.sina.com website said about 30,000 people had been evacuated. The injured had swollen and sensitive eyes and some had difficulty standing, it said.

Xinhua said the gas well burst on Tuesday, spewing a high concentration of natural gas and sulfurated hydrogen 30 meters (100 feet) into the air at the Chuandongbei field, which is owned by China National Petroleum Corp (CNPC), parent of oil major PetroChina.

It was also unclear why the reported death toll had shot up two days after the accident. Earlier yesterday Xinhua reported that 133 had died but soon raised that to 163 and then 191.

Another CNPC official in Beijing said the blast had not caused a fire.

In Kaixian, about 1,000 km (620 miles) west of Shanghai with a population of about 1.5 million, more than 200 people were being treated for poisoning, a hospital administrator said. It was not clear how many were admitted to other hospitals.

State radio said an earlier burst had been brought under control on Wednesday. It quoted a government official as saying the gas well that had burst would be sealed on Friday.

The central government sent a team to coordinate the rescue.

Chongqing and the neighboring province of Sichuan are among China's major natural gas producing areas.

In August, PetroChina began construction of a $400 million pipeline to pump natural gas from Chongqing to central China.