At least 21 people died in a fire at a mine operated by northeast China's biggest state-owned coal company, state media reported on Saturday, the latest accident in the country's trouble-plagued resources sector.

The fire broke out late Friday evening at a mine operated by state giant Longmay Mining Holding Group in Heilongjiang province's Jixi city, said the Xinhua news agency, which earlier reported 22 miners were trapped.

Longmay is the biggest coal firm in northeast China, but has struggled with financial difficulties, China Business News has reported. The Xinghua mine, where the accident occurred, is located close to the border with Russia.

Rescue workers had already found the bodies of 21 miners and were searching for one other missing person, Xinhua said, quoting the local government.

A total of 38 miners were underground when the fire broke out and 16 managed to escape. The fire originated with a long conveyor belt used to carry materials which was set at a steep angle, local media reported.

The precise cause of the fire was under investigation, state broadcaster China Central Television said.

China -- the world's largest producer of coal -- is grappling to improve standards in the poorly regulated sector. Many accidents are caused by corrupt bosses seeking profits over worker safety.

Accidents in Chinese coal mines killed 931 people last year, a top work safety official said in March.

In July, rescuers pulled six men from a flooded coal mine in Heilongjiang after they survived a week underground following an accident that killed at least four others, according to state media.

In a separate incident, 11 miners who were trapped in a coal mine in the southwestern province of Yunnan after a "cave-in" were brought to safety in July after nearly two days of rescue efforts.