Nearly 150 miners were feared killed by a gas explosion in a coal shaft in central China, the highest toll in a series of recent mine tragedies affecting the country's hard-pressed energy industry, the government said Thursday.

The blast occurred Wednesday at the state-owned Daping mine, near the city of Xinmi in Henan province, 400 miles southwest of Beijing. Gas had built up suddenly in an excavated area where night-shift workers were digging coal more than 650 feet below ground, China's official media quoted local officials as saying.

Henan's vice governor, She Jichun, told reporters that 446 people were in the mine when the explosion occurred, of whom 298 clambered to safety and 148 were unaccounted for. "According to our experience in past coal mine disasters, if we say 148 miners are missing, they probably don't have much of a chance to come out alive," Sun Huashan, the Work Safety Administration's deputy director, said at a news conference.

In response to the blast, the Work Safety Administration pledged a new crackdown on mines operating without authorization and on larger mines that often exceed production safety levels to keep up with demand for coal in China's booming, electricity-starved economy.

The Daping mine, part of the Henan Zhengzhou Coal and Electricity Co., was rated a medium-size mine, with 4,100 employees, and operated under government authorization, the New China News Agency said.

Lax monitoring and dangerous conditions in Chinese mines -- which are rated the world's deadliest -- have become a serious issue for the government, with officials repeatedly vowing to enforce safety regulations. "We can stop this problem," Sun said.

The last known mining accident of comparable magnitude in China occurred in July 2002, when 115 workers were killed at a mine in Jixi, a town in northern Heilongjiang province near the border with Russia. That mine had been ordered closed at least seven times because of safety violations but kept operating until the accident, according to the official People's Daily newspaper.

Another mining accident in Henan province killed eight workers last Sunday.

More than 6,700 miners were killed in accidents last year, according to government tallies. More than 4,000 have been killed so far this year, officials said, as mining companies cut corners in an effort to respond to growing demands for coal to feed generators supplying the country's overburdened electricity grid.

Until Wednesday night's disaster, the lower accident rate in 2004 had been praised as a sign that the government campaign to enforce safety rules more stringently was having an effect. Sun told reporters that more than 5,000 factories and mines had been closed so far this year because of safety violations.

But the owners of small, unauthorized mines have sometimes kept accidents secret to prevent authorities from shutting them down, according to industry experts, so the actual number of accidents may be higher than the official figures. Sun said his inspectors had discovered six attempts to hide mining accidents so far this year.

In addition, experts have said, some mines closed by safety inspectors have reopened after official closings, drawn into illegal operation by the strong demand and high prices for coal. With large numbers of workers laid off by failed state-owned enterprises, including mines of the now-abolished Coal Ministry, the outlaw mines have found little difficulty hiring, even though the danger is well-known.

Miners wait for news of colleagues stranded in the Daping coal mine in central China. Officials said night-shift workers were more than 650 feet below ground when gas exploded.