Xinhua reported the leak - at Qunli mine in Guizhou Province - was detected on Thursday morning when 86 miners were in the shaft.
Rescue efforts pulled 53 miners from the shaft, seven suffering injuries and one dying after emergency treatment.
The news agency said the cause of the gas leak was not immediately known and a rescue effort was launched for six miners still down the shaft.
A Reuters report confirmed the bodies of the six missing workers were retrieved from the mine during the weekend and investigations into the cause of the gas leak continue.
