The gas explosion occurred late on Friday at the Liushenyu coalmine in Qinyuan county, with 247 workers on duty underground, state media Xinhua reported.
Chinese President Xi Jinping called for authorities to "spare no effort" in treating the injured and conducting search and rescue operations, while ordering a thorough investigation into the cause of the accident and strict accountability in accordance with the law, according to Xinhua.
Premier Li Qiang echoed the instructions, calling for timely and accurate release of information and rigorous accountability.
Rescue operations were ongoing and the cause of the accident was under investigation, according to the local emergency management authority in Qinyuan.
China has significantly reduced coalmine fatalities - often caused by gas explosions or flooding - since the early 2000s through more stringent regulations and safer practices.
The Liushenyu incident, though, was one of the deadliest reported in China in the past decade.
Executives of the company responsible for the mine have been detained, Xinhua reported.
Earlier, Xinhua had reported only eight dead, with more than 200 people brought safely to the surface.
It did not explain the jump in the death toll.
12°C