The cause of the gas leak was not immediately known.
 
The government warned recently that China's mining industry, the most dangerous in the world, would likely see more accidents as output was boosted to provide heating fuel for the winter months.
 
China's coal mines average 13 deaths a day in fires, explosions and floods, despite government efforts to improve safety.
 
In August, 181 miners died when two mines flooded in eastern Shandong province after heavy rains.