The accident took place when 12 miners were tunnelling a mine shaft at the Bailongshan Coal Mine at Qujing city in Yunnan Province, spokesman with the city's emergency response office.
Three of them were lifted out of the shaft, said a spokesman with the city's emergency response office, he said.
Rescuers are trying to reduce the gas density to save the trapped miners, state-run Xinhua news agency reported.
The cause of the accident is being investigated, the report said.