SHIJIAZHUANG -- Four miners were confirmed dead after they were poisoned by carbon monoxide in a coal mine in north China's Hebei Province on Tuesday, according to local workplace safety authorities on Wednesday.

The poisoning accident occurred at 5:20 p.m. Tuesday when seven miners were working in the Yuequan Coal Mine in Chengde city which is 224 km to the northeast of Beijing.

Rescuers transported all the miners out of the coal mine as of 6:10 p.m. Wednesday. Three miners survived and four others confirmed dead, according to the Hebei Provincial Workplace Safety Supervision and Management Administration.

Cause of the accident is being investigated.