A coal mine blast in southwestern China has left 12 people dead and two more injured, The Associated Press reported.

The gas explosion occurred Friday, May 10 night in Pingba county in Guizhou province. According to the official Xinhua news agency, it says the coal mine was operating illegally and that the operators lied about the number of trapped miners and deaths. An investigation is under way.

A work safety official from the city of Anshun, which administers Pingba, says the mine is licensed and operates privately. The official gave only his last name of Lin, as is customary among low-level Chinese government employees.

China’s mines are the deadliest in the world. Authorities have tightened safety in recent years, but regulations are often ignored.