At least 20 miners were confirmed dead as rescuers on Sunday recovered their bodies trapped in Saturday's gas explosion in a coal mine in Linfen, in Shanxi Province.
The fate of 10 other miners is still unknown.
Zhao Tiechui, director of the State Administration for Coal Mine Safety Supervision, has asked the rescuers to continue search for the missing while ensuring their own safety.
"Rescue work is quite difficult since the shaft is still filled with smoke," said Zhao.
"The smoke inside the shaft is so thick that it's very difficult for us to go down to look for those still trapped," said a rescuer.
A gas blast occurred around 1.50 pm on Saturday at Pudeng Coal Mine in Kecheng Township of Puxian County where 125 miners were working.
Ninety-five miners, including 23 who were injured, escaped, said a press release by Shanxi Provincial Bureau of Work Safety.
Bureau sources said the coal mine had been earlier ordered to suspend production but mine operators resumed production on Friday without a permit.
"The coal mine was in a mess and under poor management," said the provincial work safety watchdog, adding that five different mining contractors had hired the 125 miners were working underground at the time of the blast.
Local police have put the coal mine owner and several managers under surveillance.
The cause of the gas explosion is being investigated.