The explosion occurred in a dust collection device at a cement production line belonging to Qinghai Salt Lake Haina Chemical Company, said Liu Yunzhou, head of the administration commission of Ganhe Industrial Park in the Xining economic and technological development zone.
As many as 26 workers were present on the site when the explosion took place. Two died on the spot and 12 others were injured. Four of the injured later died in hospital.
The other eight are receiving treatment. Search was on for a missing worker.
The company started production in 2013 with a daily capacity of 2,500 tonnes of cement.