China's mines are the world's most dangerous with more than 3,000 deaths a year in fires, floods and explosions.
The pre-dawn blast occurred while 436 workers were in the Tunlan Coal Mine in Gujiao city near Taiyuan, the capital of Shanxi province, the official Xinhua News Agency said.
At least 73 miners died, said a State Administration of Work Safety duty officer who would only give her surname, Zhang. She said the cause of the explosion was still being investigated.
Xinhua said 113 others were hospitalized, including 21 in critical condition. It did not say how many workers remained trapped in the shaft but earlier reports said at least 65 were still underground.
The injured miners were suffering from carbon monoxide poisoning, Xinhua reported, citing doctors at a nearby hospital. Exposure to carbon monoxide, an odorless, colorless gas, can lead to death.
State television CCTV showed rescuers in orange suits and red helmets with headlamps entering an elevator to be lowered into the mine shaft, while others emerged from the mine carrying workers on stretchers toward waiting ambulances.
Nearly 100 rescuers were on site, but their work was hampered by flames still burning in the shaft, CCTV said.
The mine is owned by Shanxi Coking Coal Group, China's largest producer of coking coal, which is used in the production of steel. The company operates 28 mines.
The Tunlan mine has some of the best facilities in the country and had not reported any major accidents in the past five years, Xinhua said. It produces 5 million tons of coking coal a year.
Xinhua quoted a rescued miner, Xue Huancheng, as saying while lying in a hospital bed that he remembered being ordered to flee when the explosion occurred.
"At that time power supply underground was cut off and we had to walk," he said, adding that he began to feel faint as he was about to reach the exit after walking about 40 minutes.
Relatives of the trapped workers gathered in the mine compound to wait for news. Some relatives had received calls on their mobile phones from miners trapped underground, Xinhua said.
The death toll was the highest in a coal mine accident since December 2007, when, according to the State Administration of Work Safety. That blast was triggered by an accumulation of gas in an unventilated tunnel.
The government has promised for years to improve mine safety, but energy-hungry China depends on coal for most of its power.
More than 1,000 dangerous small mines were closed last year, but the country's mining industry remains the world's deadliest. About 3,200 people died in coal mine accidents last year, a 15 percent decline from the previous year.
While China's overall coal mining safety record is abysmal, the numbers mask great disparities. Large, state-run mines tend to have safety records approaching those of developed countries while smaller mines have little or no safety equipment and weak worker training.
Government figures show that almost 80 percent of China's 16,000 mines are small, illegal operations.