CHONGQING - A coal mine accident that killed 22 miners Tuesday in Southwest China's Chongqing Municipality was caused by a gas explosion, authorities said Friday.

Preliminary analysis showed that the accident was triggered by a gas explosion on the goaf, or the deserted part of the mine already cleared of minerals, according to the municipal government of Chongqing.

The accident happened in the Yanshitai coal mine in Wansheng District on Tuesday afternoon when 28 miners were working in the shaft. Six of them managed to escape, with two injured in the process.

The Chongqing Municipal Administration of Coal Mine Safety earlier reported the accident as a "gas incident."

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

Further investigation into the exact cause of the accident is still under way.