Some 100 miners have been rescued.
The accident happened on 27 November at a mine in Heilongjiang Province, not far from the Russian border with Siberia.
China's mines are regarded as the most dangerous in the world. The problem has worsened as demand for raw materials has escalated to help fuel the nation's rapid economic growth.
More than 6,000 miners died in accidents in China last year, according to government figures. Independent estimates say the real figure could be as high as 20,000.