The blast rocked the state-owned Chenjiashan coal mine in Shaanxi province at 7:20am, when 293 workers were underground, the official Xinhua News Agency said. The explosion was centered around coal pits five miles from the mine entrance, it said.
At least 166 workers remained trapped, while 127 escaped, Xinhua said, citing the State Bureau of Production Safety. Most who escaped were working close to the entrance and many suffered from carbon monoxide poisoning - some 41 were hospitalised, Xinhua said.
Witnesses said they saw "huge amounts of thick smoke pouring from the mine's ventilation vents," hampering rescue efforts, according to the website of the Communist Party's People's Daily newspaper.
Staff at Chenjiashan said communications with the trapped miners were cut off, the site said.
On its evening newscast, state television showed ambulances rushing to the scene as huge crowds of people gathered outside the main gate of the mine.
President Hu Jintao urged rescuers to employ "all effective measures" to save the trapped workers, China Central Television said.
China's mines are the world's most dangerous, with thousands of deaths reported every year due to explosions, fires, cave-ins and flooding often blamed on lax safety rules and lack of required equipment.
The government has vowed to improve conditions and frequently orders mass shutdowns and safety checks after a fatal mine accident. But despite the crackdown, accidents still happen on a near daily basis. Chinese officials have suggested a countrywide energy shortage may be pressuring the mining industry to raise coal production.
The worst mining accident in four years occurred last month, when a massive explosion in the Daping Mine in central Henan province killed 148 people.
It was sparked after mine operators failed to realise that extending the mine's shaft would greatly increase its gas level.
Also Sunday, 16 officials in the northern Hebei province were charged with helping to cover up a massive coal mine explosion June 3 that killed 14 miners and injured 23 others, Xinhua said.
It said the mine owner "collaborated with some local officials" to give a false death toll of one to investigators from the central government. The owner was worried that if the real figure was revealed, authorities would shut down his mine, Xinhua said. The officials' misconduct included failing to search passages for more trapped miners and secretly cremating five bodies.