Rescuers trying to reach 141 miners trapped by an underground explosion were pumping noxious fumes out of a Chinese coal mine Monday but an official said their chances of survival were "extremely slight." Another 25 miners were confirmed dead.

Early rescue efforts following the blast Sunday were blocked by high levels of carbon monoxide and thick smoke in the Chenjiashan Coal Mine (search) in the central province of Shaanxi (search), according to the government.

The mine's wrecked ventilation system was repaired by mid-afternoon Monday, the official Xinhua News Agency said, but it wasn't clear when it would be declared safe for rescuers to enter.

The gas explosion occurred about five miles from the mouth of mine.

An official at the Shaanxi coal mine safety bureau said Monday that hope was fading fast for the trapped miners.

"The rescue effort has been extremely difficult due to large concentrations of carbon monoxide," said the official, who would give only his surname, Chen. "From my own experience the odds that the 141 still underground remain alive are extremely slight."

Some 127 workers managed to escape the state-owned mine, Xinhua said, citing safety officials. Forty-five 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.

State television showed officials visiting hospitalized miners, many of whom were swathed in bandages.

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.

If none of the trapped miners survive, it would be "the deadliest accident in recent history," said a woman who answered the telephone at the State Work Safety Administration in Beijing. She refused to give her name or provide any more details.

President Hu Jintao (search) has urged rescuers to do everything possible to save the trapped miners. Premier Wen Jiabao, who was at a conference with the Association of Southeast Asian Nations in Laos, promised a thorough investigation and improved safety measures in China's mines.

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.

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.

Explosions often are blamed on lack of required ventilation equipment need to clear away gas that seeps from the coal beds.

The government said in September that the death rate in China's coal mines this year was 13 percent below the level of last year, due largely to a nationwide safety crackdown.

But accidents are still reported almost daily. Chinese officials say severe nationwide power shortages might be increasing pressure for mines to raise coal production, raising the risk of accidents.

Chinese officials have to stress the need for "a safety culture" at mines, said Kawakami, an occupational safety specialist at the International Labor Organization, the United Nations' labor agency.

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

According to Xinhua, Chenjiashan produces 2.3 million tons of coal a year.

China, the world's biggest coal producer, is expected to churn out 1.8 billion this year, according to the government newspaper China Daily.