A gas explosion at a coal mine in China has killed at least 90 people, in the country’s deadliest mining accident in recent years.

State media Xinhua said 247 workers had been on duty underground when the blast ripped through the Liushenyu mine in Qinyuan county, Shanxi province, on Friday.

China’s coal mines are considered among the deadliest in the world due to poor safety standards, weak regulation, and corruption as companies seek to profit from the country’s rapidly expanding economy.

Rescue operations were ongoing as emergency crews continued searching for survivors of the explosion.

Nine miners were still unaccounted for as of Saturday afternoon, Xinhua said, and more than 120 people were hospitalised. Among the injured, many were hurt by toxic gas, according to state-run broadcaster CCTV.

The blast occurred shortly after a carbon monoxide alert was issued, with some reports claiming gas levels had exceeded safe limits.

According to CGTN, the person responsible for overseeing the mine has been arrested while authorities investigate the cause of the explosion.

Shanxi province, where the incident occurred, is China’s main coal-mining region. More than one billion tonnes of coal were extracted there last year, almost a third of the country’s total output.