The blast happened late evening yesterday when 20 people were working inside the mine, about 120 km from Xinjiang's regional capital Urumqi. Three of them have been rescued.
Rescuers are working on to evacuate the others trapped inside the mine.
They are pouring nitrogen into the mine to dilute the gas concentration, state-run news agency Xinhua reported.
The process, which was started early morning today, needs to be continued for 24 hours before rescuers could enter the pit, the report said.