Pit gas is thought to have exploded in the coal mine run by Mittal Steel Temirtau in the Karaganda Region, southeast of the country's capital, Astana. A total of 374 people were working at the moment 620 meters (over 2,000 feet) deep. More than 300 miners managed to reach the surface after the blast.
"The bodies of 40 miners have been brought to the surface, and another miner who was in the pit at the time of the incident has not been located yet," Vladimir Selivanov said.
He said six people had been hospitalized, including two in a serious condition, and that the rescue operation was continuing. "We will work until the last man in the pit is found."
The trade union of Mittal Steel Temirtau's coal arm pledged $12,000 in compensation to the families of late miners, and prosecutors said they had opened a case into negligence.
President Nursultan Nazarbayev offered his condolences Wednesday to the late miners' families and ordered that a commission be set up to investigate the causes of the tragedy and to arrange assistance to the families.
"All Kazakhs empathize at this difficult time with the disaster that has struck the miners of Karaganda," a message from the president said.
The incident in Kazakhstan was not the only one Wednesday. In Ukraine, 13 people died following an explosion at a mine in the east of the country.
A total of 25 miners died after a blaze broke out September 7 in a Russian pit in southern Siberia.