A gas explosion at a coal mine in southern China has killed at least 29 people.

The blast occurred on Saturday night at a colliery in the Hunan province, Chinese state media reported on Sunday.

Six other miners were treated in hospital after surviving the accident at a state-owned coal mine in Hengyang city.

China's State Administration of Work Safety said in a statement on its website that five workers had been rescued while another climbed out of an air shaft.

State broadcaster CCTV said that the mine's operating license had been revoked in the first half of this year because it did not adopt measures to pump out dangerous gases from underground, but that mining had continued without permission.

Song Yuanming, the chief of the provincial coal mine safety bureau, told state broadcaster CCTV that a large outburst of gas 250 metres underground had been ignited by sparks produced by machinery.

According to the official Xinhua News Agency, the Hengyang mine has been operating legally for 40 years, with an underground workforce of 160.

Due to the high demand for coal in China, some producers sidestep safety regulations, although conditions have improved in recent years and a number of small, illegal mines have been shut down.

Conditions in Chinese coal mines are among the most dangerous in the world. Last year 2,433 people died in mining accidents, although the number of fatalities has fallen since a recent high of 7,000 deaths in 2002.

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Conditions in Chinese coal mines are considered among the most dangerous in the world [EPA]

Al Jazeera