BEIJING -- An explosion ripped through a workers' dormitory area and killed at least 15 people Saturday at a coal mine in a city in northern China notorious for mining disasters.

The cause of the 2 a.m. blast at the Liugou mine in Linfen city in the northern province of Shanxi was still under investigation, according to work safety officials at the central and provincial level. They would not give their names, as is common among government workers in China.

The state-run Xinhua News Agency said another 20 people were injured in the explosion, citing a senior official with the mine's owner, the Yangquan Coal Industry (Group) Co. Ltd.

It was not yet clear whether the mine was licensed. China has been trying to improve the safety of its mining industry, which is by far the world's deadliest, but an unknown number of illegal mines exist to profit off the country's huge appetite for power.

The website of the Yangquan Coal Industry (Group) Co. Ltd said the company is state-owned. Phone calls to the company rang unanswered Saturday.

The gritty city of Linfen is especially well-known for coal mine accidents. The city's most powerful job, that of party secretary, went unfilled for more than six months in 2008 and 2009 as officials appeared to shy away.

"The most unwanted job in the Chinese Communist Party," said the Hong Kong-based China Labour Bulletin, which tracks labor issues on the mainland, when the post was finally filled. The official, Xie Hai, remains in the job.

His predecessor was fired after a massive landslide from an illegal mining operation submerged a village under Linfen's oversight and killed at least 277 people in late 2008.

Linfen had nine major coal mine disasters, with more than 10 deaths each, between 2003 and 2008, the China Labour Bulletin reported last year.

Last year, accidents and blasts killed more than 2,600 coal miners throughout China. (AP)