Image copyright Xinhua Image caption Local media reported more than 400 workers are involved in attempts to rescue possibly trapped miners

Thirteen people were killed and another 20 remain unaccounted for after an explosion in a coal mine in China, according to state media.

The gas explosion happened on Monday morning at a privately owned mine Jinshangou in the southwestern Chongqing region, Xinhua reported.

Attempts are continuing to reach the 20 miners, who are believed to still be trapped, the news agency said.

Mine accidents are common in China, despite efforts to improve safety.

In January, four miners were rescued from a collapsed gypsum mine in Shandong province after 36 days trapped underground. The mine's owner killed himself shortly after the accident.

Image copyright Reuters Image caption Rescuers worked through the night

"We are still working all-out to search for the 20 missing miners, and will exert our utmost as long as there's still a ray of hope," Chongqing Deputy Mayor Ma Huaping said of the Jinshangou explosion.

Two men are reported to have escaped unharmed.

Local authorities have ordered an investigation into the incident and ordered smaller coal mines in the region to close temporarily.

China is the world's largest producer and consumer of coal. The Jinshangou mine is licensed to produce 60,000 tonnes of coal a year, local media said.