A Fushun police officer told AP the explosion in late March was caused by the build up of gas after the power was shut off to adjust the voltage.

The manager of the Mengjiagou mine, He Wanku, and depute mine manager Zhu Yi, were detained on charges of violating work rules.

The police officer said the managers failed to order the mine evacuated after shutting off equipment that kept the shafts clear of gas escaping from the coal bed.

China's coal mining industry has a history of fatalities from gas explosions, and officials have repeatedly pledged to improve the safety of the industry through closing illegal mines.

Earlier in March in a separate coal mine gas explosion in northern China at least 50 people were killed.