A gas leak caused a fire at a state-owned natural gas well in northwest China's Shaanxi Province last Friday, and the fire continues to burn, authorities said Thursday.

The accident happened at 11:20 p.m. on July 23, as workers drilled a gas field 2,750 meters underground in Yanchang County.

The accident happened at 11:20 p.m. as workers drilled a gas field 2,750 meters underground in Yanchang County, said Wang Fujian, a county government publicity official.

The well is operated by Yanchang Petroleum Group.

Fire fighters said the gas leak was nitrogen sulfide and carbon monoxide.

Experts from southwestern China's Sichuan Province, a major natural gas production base, have been called in to help extinguish the fire and cap the leak.

Residents from five villages in Qilicun Town, Yanchang County, Yan'an City, were evacuated shortly after the explosion.

"Witnesses said they heard loud bangs and saw flames soar at least 20 meters into the air," said Wang.

"Some villagers said they could feel the heat 200 meters away from the site. One villager was about to go to bed when he heard the village loudspeaker order everyone to immediately flee. Some villagers, already in bed, ran out without getting dressed properly."

The evacuated villagers have not yet been able to return to their homes.