An accident in a northern Chinese coal mine has left 21 miners dead, state press reported Monday, citing a local provincial mining bureau.

The cause was not immediately clear but miners were first reported trapped in the mine in one of China's prime coal producing areas on Saturday morning, the China News Service said.

Twenty-one were confirmed dead in the mine in Datong city, Shanxi province, while 11 others either escaped themselves or were rescued, it said.

According to the China Daily, preliminary investigations showed that either a gas blast or a spontaneous ignition were the likely causes of the accident.

Victims suffered from carbon monoxide poisoning, it said.

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 the huge demand for coal -- the source of about 70 percent of China's energy.

Nearly 3,800 lives were lost in Chinese coal mines last year, down 20 percent from the year before, according to official figures.