At least 90 people were killed after a gas explosion occurred at a coal mine in China’s northern Shanxi province, according to state media reports Saturday.

China’s official Xinhua News Agency said the blast occurred Friday evening at the Liushenyu coal mine in the city of Changzhi. About 247 workers were on duty at the time of the accident.

Initial reports from Xinhua early Saturday said eight people had been confirmed dead and 38 miners remained trapped underground. By Saturday afternoon, state media said nine workers were still trapped as rescue operations continued.

Authorities said the cause of the explosion remains under investigation. State broadcaster CCTV reported that many of the injured suffered from toxic gas exposure. Rescue crews are searching the mine Saturday.