At least 22 workers have been killed during a gas explosion at a coal mine in China's southwestern municipality of Chongqing.

Regional authorities say the accident, which reportedly occurred at 5:40pm local time at the Yanshitai Coal Mine in Wansheng District, was caused by a "gas incident"

"I heard a big sound of gas explosion over the steps," said He Xiaogang, one of the injured miners.

"(I realized) something horrible happened, and we escaped the shaft from where thick smoke was coming out."

The Chongqing Municipal Administration of Coal Mine Safety said a total of 28 miners were working down the shaft at the time of the accident. Six of them managed to escape, with two injured in the process.

Doctors at a local hospital treating injured miners said that the miners sustained burns and carbon monoxide poisoning during their escape from the mine.

Local authorities are dealing with the aftermath of the accident, including an investigation into the cause of the accident.

The state-owned Nantong Mining Co Ltd, which owns the mine, is yet to comment on the incident.

China's mines are considered the deadliest in the world because of lax enforcement of safety standards and a rush to fuel demand from a rapidly growing economy.

Reuters