Cao Yaofeng, vice president of China Petrochemical Corporation, and experts from Beijing have arrived at the leaking well site in Sichuan Province and are working on a second plan, said Zhang Chongyao, a spokesman of Xuanhan county government.

The leakage occurred around 7:00 p.m. Thursday at Qingxi No. 1 Gas Well in Qingxi Town, Xuanhan County, according to Yu Longhai, an official with Dazhou city government.

Emergency workers set fire in four sites 100 meters from around the leaking well to alleviate the harmfulness of the gas, about three hours after the leakage.

More than 12,000 residents in eight villages were evacuated to safety, and no casualties have been reported, said Yu.

The evacuated went to their relatives or were arranged to stay in township government's meeting rooms, schools or broadcasting stations, according to Wang Nengqiu, Magistrate of Xuanhan County.

A first capping plan, which was carried out at 1:10 a.m. Sunday, was announced a failure due to complicated conditions under the well.

"About 300 cubic meters of mud was infused into the well in the first capping, but no effect is achieved," said He Shenghou, deputy chief of the emergency headquarters at the site.

Flames of fires are still 20 to 30 meters high around the well, according to emergency crew.

Tests of leaked gas contained no sulfureted hydrogen, which is harmful to people, local environmental authorities said, adding that sulfur dioxide was not found either in the air.

More than 400 primary and middle school students, who were evacuated in the accident, will resume classes on Monday, according to local education authorities.

Residents who live 500 meters or further from the well began to go back home Sunday afternoon and those within a radius of 500 meters around the well will continue to stay where they are, according to town government officials.

The emergency headquarters have not decided when to carry out the second capping plan.

Xuanhan County, about 500 kilometers northeast of Chengdu, capital of Sichuan, is one of China's important proven natural gas bases. The country has begun to pour huge investment into the development of its rich gas resource.