The death toll in a coal mine explosion in central China (search) rose to 63 with 103 workers still missing, the government said Tuesday, as toxic fumes unleashed from the blast slowed rescuers from entering the pit.

Rescue workers have recovered 63 bodies from the Chenjiashan Coal Mine (search) in Shaanxi, the official Xinhua News Agency said, citing Huo Shichang, an official from the provincial coal industry administration.

Hopes were fading for some 103 miners still missing. If none of the missing survives, it would be one of the deadliest disasters in a decade to hit China's accident-prone mining industry.

Emergency workers descended into the mine Monday to repair ventilation systems needed to pump the fumes out, Xinhua said. But the agency didn't say whether rescuers had begun making their way in to search for the miners, and officials reached by phone said they didn't have any more details.

"After safe conditions are ensured, then rescue efforts can be sped up," Xinhua said late Monday.

Survival chances for the missing miners were "extremely slight" because of high levels of carbon monoxide, said an official of the mine safety bureau in Shaanxi (search) province, where the mine is located. Contacted by phone, he would give only his surname, Chen.

"We have to look after the safety of the rescuers," Chen said. "If they take oxygen tanks down there, there could be another explosion caused by a leak. But if they don't take oxygen down they'll die in a second."

Premier Wen Jiabao, at a meeting of Asian leaders in Laos, said he was "extremely upset" by the disaster. President Hu Jintao urged rescuers to spare no efforts to find the missing miners, state television reported.

The television footage showed stacks of blue oxygen tanks waiting to be used and government officials studying blueprints of the mine as they organized rescue efforts.

Photos released by Xinhua showed weeping relatives and a miner, his face and hands blackened with soot, being carried out on a stretcher surrounded by officials and rescue workers in red hardhats.

Some 127 miners managed to escape, Xinhua said, citing safety officials. Among them, 45 were hospitalized, 11 with serious injuries.

One rescued miner was quoted by Xinhua as saying he was knocked down by the shockwave from the explosion, which occurred some five miles from the mouth of mine.

The accident came just weeks after another coal mine explosion killed 148 people elsewhere in central China — the highest death toll in a mining accident since 2000.

China's coal mines are the world's deadliest, with 4,153 people reported killed in the first nine months of this year in fires, floods and other disasters. The government says Chinese mines accounted for 80 percent of all coal mining-related deaths worldwide last year.

Authorities have repeatedly vowed to do more to stop the carnage by boosting safety measures and punishing negligent mine owners. But accidents are still reported almost daily. Officials say severe nationwide power shortages might be increasing pressure for mines to raise coal production, boosting the risk of accidents.

China, the world's biggest coal producer, churned out 1.6 billion tons of coal in the first 10 months of this year — up 19 percent from the same period last year.

Officials need to promote "a safety culture" at mines, said Tsuyoshi Kawakami, an occupational safety specialist at the International Labor Organization, the United Nations' labor agency.

He recommended daily inspections to find potential risks.

"Big accidents can happen because of multiple small factors, because of poor maintenance," he said.