BEIJING -- Thirteen people have been trapped in a coal mine in north China following an explosion, state media reported Saturday, in the country's third mining accident in two days.

The blast happened on Friday in a mine that had stopped production in Hebei province's Tangshan city, trapping nine maintenance staff, the official Xinhua news agency reported. It did not explain why the men were in the mine at the time.

The owner of the mine sent four people into the mine to rescue the trapped workers, but they also went missing, Xinhua said, quoting local police.

Rescue operations were underway, according to the report, and there was no mention of the condition of the workers.

The local work safety bureau and police were not immediately available for comment.

The accident comes after at least 39 people were killed in two separate coal mine explosions in the northeast and southwest on Thursday and Friday.

China's coal mines are among the most dangerous in the world, with safety standards often ignored in the quest for profits and the drive to meet surging demand for coal -- the source of about 70 percent of the country's energy.

Nearly 3,800 people died in Chinese coal mines last year, according to official figures, although independent monitors say the real figure is likely to be higher as many accidents are covered up.