BEIJING - Rescuers trying to reach 141 miners trapped by an underground explosion were pumping noxious fumes out of a Chinese coal mine today, 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 in the central province of Shaanxi, according to the government.

The mine's wrecked ventilation system was repaired by mid-afternoon today, 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 today 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.

President Hu Jintao 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.

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.