A huge subterranean gas explosion has ripped through a Chinese coal mine Sunday morning in what may be China's worst mining disaster in years. Massive fatalities are expected, as rescue workers try to free at least 170 miners still trapped deep underground.

It could be the worst disaster to hit China's notoriously dangerous mining industry in years.

Official media report just fewer than 300 miners were in the state-run Chenjiashan complex when an underground explosion tore through the mine about 7:30 Sunday morning.

Witnesses report seeing black smoke pouring out of the mine's ventilation shafts.

At least 123 people emerged immediately after the blast - reportedly eight kilometers from the shaft's entrance. The mine is located about 700 kilometers southwest of Beijing in Shaanxi Province.

China's coal mining industry has been the focus of intense safety concerns following a series of tragic accidents.

An October gas explosion killed 148 workers at a mine in Henan Province, the worst incident since 2000.

Those fatalities prompted Sun Huashan, deputy administrator of China's Work Safety Administration, to admit last month that serious safety flaws are still an issue in China's coal industry.

"This has exposed the many problems that exist in our work, such as the fact that fundamental facilities of coal mine work are still very weak."

Chinese officials insist the state is now working overtime to improve mine safety.

Beijing has set aside nearly half a billion dollars to help local and state-run mines monitor and prevent gas explosions.

In all, more than four thousand people have died in China's coal mine operations this year, down about 15 percent from 2003.

Nevertheless, China's mining industry remains the world's deadliest, accounting for roughly 80 percent of all mine fatalities around the world.

And critics warn China's massive energy needs only increase the pressure on mine operators to produce more coal, more quickly and on limited budgets.

As a result, they say safety is often the first casualty as owners try to maximize profits and meet rising national demand.