Xinhua reported that 11 workers suffocated while trapped underground at a mine construction site in the Shuocheng district of the Shanxi province, in the country’s north, on Saturday.

The cause of the accident remains unclear.

On Friday, New Tang Dynasty Television reported the death of 10 coal workers following an explosion at an underground mine in Yunnan province, southwest China.

The television station said the cause of the explosion was being investigated.

China has been the only nation which has increased its coking coal imports so far this year.

According to Goldman Sachs JBWere, this was partly due to local government clampdowns on unacceptable health and safety standards across the small mine sector, which produces the majority of China’s coking coal.

Government officials were forced to change coal mining regulations after an underground gas explosion at the Tunlan Colliery in northern Shanxi Province killed 78 people and injured 114 in February, receiving considerable media attention around the world.