The gas explosion hit the Jiaojiazhai mine in coal-rich Shanxi province near midday on Sunday, the official Xinhua news agency said.
By late on Sunday night, rescuers had found 17 bodies and 30 were still trapped in the mineshaft, their fate unclear, the semi-official China News Service said.
The chief of China's work safety authority, Li Yizhong, arrived at the mine on Sunday night to oversee rescue efforts, it added. But recuers' efforts to reach the other trapped miners were impeded by dense gas and collapsed tunnels, it said.
The mine belonged to the Shanxi Tongmei Group, and was known for its high accumulation of gas, according to the China News Service.
China is struggling to meet booming demand for coal, which fuels about 70 percent of its energy consumption.
In the rush for profits, safety regulations are often ignored, production is pushed beyond limits and dangerous mines that have been shut down are reopened illegally.
Despite a 23 percent decline in the death toll from mine accidents in the first nine months of 2006 compared with the same period of the previous year, 3,284 coal miners have died in more than 2,000 accidents through September.
End-of-year pressure on mines to meet orders and production goals encouraged mine operators to neglect safety, Xinhua said.

Copyright Reuters, 2006