The incident happened at about 2 p.m. Friday at the Liangshuigou Coal Mine in Muzhuo Township of Zhenxiong county, China's Xinhua news agency reported.
An initial investigation into the incident found a gas blast to be responsible.
The manager of the mine said 20 workers were inside at the time of the blast. Twelve of them had been lifted out of the mine before the accident.
The manager of the colliery has been in police custody.