The accident took place around 8 am (local time) at Zhaojin Coal Mine in Yaozhou District when 67 workers were in the shaft, a spokesman with the Tongchuan city government told state-run Xinhua news agency.
Fifty-six people managed to escape and the rest are still missing. Rescue operations are underway to find the missing ones.
At least 10 people were killed and 40 others were reported missing in two separate accidents at coal mines in China in August last year.
The risk for coal-mining accidents in China is one of the highest in the world.
According to a 2003 government report, the coal miners' death rate per one million population was about 37 times that of America's coal-mining death rate.