Around 35 miners were inside the mine in Chongqing Municipality when the explosion occured yesterday morning.
Fifteen miners were still missing and rescue work was underway, state-run Xinhua news agency reported.
Two workers escaped unharmed, leaving 33 trapped in a pit at Jinshangou Coal Mine, Yongchuan District.
The police were looking into possible misconduct by the mine's management team, said Luo Qingquan, head of the district government.
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At least 20 ambulances and dozens of medical workers were on standing by.
When the explosion occurred, Tao Puzhang, 60, working on his land about 500 metres from the mine, heard a big noise and felt the ground shake under his feet.
Liu Fuxiu, a winch operator with the mine, working 40 metres from the entrance to the pit, was knocked off her feet by the blast and received injuries to her face and back.
"My injuries are nothing," she told the news agency. "I have a relative down the pit and I hope he is alive."
The mine has a designed annual output of 60,000 tonnes, according to its license.