The mine, which opened in 2004, was closed for failing to meet safety standards. On Sunday, a group of workers tried to restart coal production in the mine, and two hours later the blast followed.
The rescue operation has been completed at the mine, where the accident occurred late on Sunday in the city of Linfen. Police are searching for those behind the illegal mining operation.
China's coal mining industry is considered the world's most dangerous with over 3,000 people killed each year in fires, floods, explosions and rockfalls. The deadliest accidents usually occur in small privately-owned mines in autumn and winter as owners increase coal production during the winter season.