Rescuers wait to go underground after a gas leak hit a coal mine causing at least 21 miners killed and 16 still trapped in Yuzhou city, Central China's Henan province, on Oct 16, 2010. [Photo/Xinhua]

YUZHOU - Scores of rescuers on Saturday night slowly made their way through dust-filled underground tunnels to continue searching for 16 miners who were trapped following a coal mine gas leak in central China's Henan province.

Twenty-one miners have been confirmed dead in the accident, local work safety authorities said, while 239 out of the 276 miners who were working underground escaped after the gas leak occurred at about 6 am in a small coal mine in Yuzhou city.

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"The thick dust in the shaft is hampering the rescue. We must clear the dust first. We have located the trapped miners already," said Du Bo, an engineer with the mine's parent company who participated in the rescue.

He said more than 2,500 tonnes of coal dust were in the pit due to damage caused by the gas leak.

The conditions of the missing miners remains unknown. Officials said the miners were located 50 to 80 meters down the shaft from the entrance to the pit.

"Fortunately, there was no gas explosion. Otherwise, the consequence would be disastrous," a rescuer surnamed Wang told reporters. He said most of the victims were believed to have suffocated.

Officials said work crews are struggling to retrieve the remains of the victims from the mine.

The mine is owned by Pingyu Coal & Electric Co Ltd, a company jointly established by four investors, including Zhong Ping Energy Chemical Group and China Power Investment Corp It was hit by a similar gas and coal leak in 2008. Twenty-three people died in that accident.

Luo Lin (L), director of the State Administration of Work Safety, supervises the rescue work of the trapped miners after a coal mine accident, in Yuzhou city, Central China's Henan province, Oct 16, 2010. [Photo/Xinhua]

Ironically, miners were working underground to improve accident prevention measures when the gas leak occurred on Saturday.

Billboards reading "Safety is a fortune of the family; Safety is of heavenly importance to our miners" hung at the entrance of the mine.

Guo Gengmao, governor of Henan, and Luo Lin, head of the State Administration of Work Safety, supervised the rescue efforts.

Authorities are investigating the cause of the gas burst.

The accident occurred as people around the globe watched in awe during the rescue of 33 Chilean miners trapped underground for more than two months. China's work safety officials and experts said there are lessons to learn from Chile's dramatic rescue.

"Mining accidents in China usually claim heavy loss of lives. The lack of modern emergency response systems is a key factor," said Liu Tiemin, a researcher with the China Academy of Safety Sciences and Technology.

Gas leaks in China's coal mines left 341 people dead in the first half of this year.

Of note, the fatality rates have actually decreased in recent months as the country's senior officials ordered the industry to strengthen safety measures.

China closed 7,466 illegal mines in four years, from 2006 to 2009. Mine operators are required to obtain all operational permits and have safety systems installed.