A gas explosion at a mine in northern China has left 21 workers trapped, the government's work safety agency said on Wednesday.
The accident occurred just after midnight on Sunday in Shanxi province but local officials failed to immediately report the accident, the State Administration for Work Safety said on its website.
The site of the accident, the Miaojiang coal mine, is near Jincheng city in Shanxi, China's coal mining heartland, it said.
China's mines are the most dangerous in the world with 4,746 miners dying in 2,845 accidents last year, according to official figures.
Independent labour groups put the death toll at as many as 20,000 miners annually, as mine operators often cover up accidents to avoid costly shutdowns and fines.