At least 127 miners escaped from the state-owned Chenjiashan Coalmine in Shaanxi province after Sunday morning's explosion, the official Xinhua news agency said, but other state media reported different numbers.
The People's Daily, mouthpiece of the ruling Communist Party, said on its website 85 had escaped.
"Workers at the mouth of the Chenjiashan coal mine discovered thick smoke pouring out of ventilation shafts, and that communication with the inside of the mine had been cut off," the People's Daily said.
Rescue workers had advanced several hundred metres into the mine but were blocked by heavy smoke, state media said. Doctors from nine hospitals were taking part in the rescue.
Xinhua said some 140 miners were still trapped.
An official contacted at the mine, near the city of Tongchuan about 740km southwest of Beijing, said he had no information about the cause of the blast or casualties. Several other government officials declined to comment.
China's coal mine industry, which provides the primary fuel for the world's seventh-biggest economy, has a dismal safety record that has been grimly underscored by a series of major accidents this year.
China is the world's seventh
A coal mine blast in the central province of Henan this month killed 33 miners. That followed an October explosion, also in Henan, that killed 148 miners.
Online comments on Xinhua's website (www.xinhuanet.com), bemoaned the state of an industry that killed 4153 workers in the first nine months of this year.
"Why do these accidents keep happening one after another? Why don't the relevant authorities do something about it? Why don't we just kill a bunch of officials? Are Chinese people's lives worth less than money?" asked one person in an anonymous posting to the site.
Beijing has tried to clamp down on safety violations at many mines, and official figures show coal mine deaths in the first nine months were down by 630, more than 13% from the same period a year earlier.
The Chenjiashan Coalmine, administered by the Tongchuan Mining Administration of Shaanxi Province, is capable of producing 1.3 million tonnes of coal a year, Xinhua said.