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.