The death toll in a mine blast in central China has climbed to 23, state media reported on Monday.
Seven others are still missing from the explosion on Saturday afternoon at the Pudeng coal mine in Shanxi province.
"Rescue work is quite difficult since the shaft is still filled with smoke," Zhao Tiechui, director of the State Administration for Coal Mine Safety Supervision, was quoted as saying.
China's mines are the deadliest in the world, with an average of 13 miners dying every day in accidents. With coal prices high to feed the booming economy's energy demand, mine operators often ignore safety regulations to boost production.
The Pudeng mine, outside of Linfen city, had been ordered to suspend production for unspecified reasons, but the mine's operators resumed operations without a permit.
Local police have placed the mine's owner and an unspecified number of its managers under surveillance. About 125 miners, hired by five different contractors, were working underground at the time of the blast.
It was the second blast in a week in Shanxi, China's largest coal-producing province.
Last Monday, a blast in an illegal mine in Yuxian county, killed 14 people. Two owners of the mine fled after the accident.