CHONGQING, June 4 -- The investigation has begun into a coal mine accident that left 22 miners dead in southwest China's Chongqing Municipality on Tuesday evening.

A gas blast hit the Yanshitai coal mine in Wansheng District at about 5:40 p.m., miners who survived the accident said. The Chongqing Municipal Administration of Coal Mine Safety earlier reported it as a "gas incident."

A total of 28 miners were working down the shaft at the time of the accident, the administration said. Six of them managed to escape, with two injured in the process.

A survivor surnamed Liu said he heard two loud bangs before a shockwave knocked him to the ground. Realizing it was an explosion, he and another miner began to run. The other miner, who Liu said had lost his lamp, might have lost his way and was later found dead in the mine.

A team led by Fu Jianhua, deputy director of the State Administration of Work Safety, arrived in Chongqing on Wednesday to oversee the investigation and other matters.

The coal mine belongs to the state-owned Nantong Mining Co., Ltd, the largest coal producer in Chongqing.