Twenty-one miners have been confirmed dead after a coal mine gas leak accident in the southwestern province of Yunnan, and hundreds of rescuers are rushing to save the 22 people still trapped underground Friday, local authorities said.

Rescuers on Thursday enter a shaft at the Sizhuang Coal Mine in Shizong county, Yunnan province, where a coal and gas outburst killed 20 people and trapped 23. [Photo / China Daily]

The deadly accident occurred at around 6:30 a.m.when an outburst of coal and methane gas hit the Sizhuang Coal Mine in Shizong county,the Yunnan Provincial Emergency Response Office said in a statement.

Forty-three miners who were working in the shaft were trapped immediately after the outburst.

By 3 pm on Thursday, at least 20 miners were confirmed dead. Rescuers were struggling to reach another 23 and were still nearly 100 meters from the position of the trapped miners, Tan Xiaopeng, head of the local fire brigade, said on Thursday afternoon.

The rescue operation involving about 30 firefighters, 100 professional rescuers and 300 medical workers is underway, the statement said.

Meanwhile, more than 30 ambulances were also on site, it said.

The search and rescue operation faces great difficulties, said Tan, because gas intensity in the shaft remains so high that it could easily ignite.

Local authorities said that the mine had been run illegally, as its safe work license was revoked on Nov 28, 2010, but it later resumed production.

Luo Lin, head of the State Administration of Work Safety, ordered local authorities to try every means to save the trapped miners.

The private mine, with an annual output capacity of 90,000 tons of coal, has a relatively poor safety record, according to the Yunnan Administration of Coal Mine Safety.

In April 2005, a fire caused by gas rocked the mine when it was under construction to expand its capacity, killing four miners in the shaft.

The accident resulted from lack of safety measures to prevent underground gas buildup, the coal mine safety administration said later in an investigation report.