The well sprayed a high concentration of natural gas and sulphurated hydrogen 100 feet into the air spreading fumes to nearby areas and causing "mass casualties," the official Xinhua news agency quoted Wu Jianong, vice mayor of Chongqing, as saying,

"The poisonous gas hovering in the air made an area of 25 sq km (10 square mile) death zone as many villagers were intoxicated by the fumes in their sleep," the China Daily newspaper said.

About 42,000 people were evacuated after the blowout and 1,000 workers were clearing away almost 4,000 animals, including cattle, pigs, rabbits, ducks, chickens and dogs, killed by the gas well burst, Xinhua said.

Eight villages are being disinfected, with drinking water and poisoned crops near the site of the leak still being tested.

Clean up crews have poured hundreds of cubic meters of mud and cement into the 1,300-foot well, plugging a mix of natural gas and sulphurated hydrogen that causes acid burns to the eyes, skin and lungs of victims.

A total of 10,175 people were either hospitalized or treated and discharged. Nearly 80 people were in serious condition.

The well where the blow-out occurred is owned by China National Petroleum Corp (CNPC), parent of oil major PetroChina. In August, PetroChina began construction of a $400 million pipeline to pump natural gas from Chongqing to central China.