HOHHOT - A limestone mine explosion on Sunday morning in north China was triggered by explosives used by locals, according to a police investigation.

The explosion, which occurred at about 2 am at Urad Front Banner in North China's Inner Mongolia Autonomous Region, has left six people missing and one person injured.

The injured person, surnamed Wang, told police that he and six other locals tried to blast a small hilltop to reach the limestone underneath using explosives made from three tonnes of compound fertilizer.

The blast occurred while they were making the explosives.

Police said no authorization has been issued to mine limestone in the area.

Wang has been sent to the hospital and local authorities are still searching for the six missing.