A sudden explosion of rock in a coal mine in central China following a small earthquake killed four miners and trapped 57 others, a state news agency reported on Friday.
The accident in the coal mine in the city of Sanmenxia in Henan province occurred Thursday evening when 75 miners were working in the shaft, the official Xinhua News Agency said. Fourteen workers escaped.
The Qianqiu Coal Mine belongs to Yima Coal Group, a large state-owned coal company in Henan, the State Administration of Work Safety said on its website.
Xinhua said a magnitude-2.9 earthquake occurred to the east of Sanmenxia and that the rock explosion happened about 30 minutes later.
The phenomenon known as a “rock burst” occurs when settling layers of earth bear down on the walls of a mine and result in a sudden, catastrophic release of stored energy. Exploding pillars can turn chunks of rock or coal into deadly missiles, and the shock waves alone can be lethal.
China’s coal mines are the most dangerous in the world, although the industry’s safety record has improved in recent years as smaller, illegal mines have been closed. Annual fatalities are now about one-third of the high of nearly 7,000 in 2002.