BEIJING, May 14 (UPI) -- A gas explosion in a coal mine in China's southwest Guizhou province killed 21 workers, rescuers said.

The blast occurred Thursday night in a shaft where 31 miners were working, Xinhua news agency reported. Rescuers reported 10 of them either escaped or were rescued. The bodies of all those killed were recovered by Friday, the report said.

The privately owned coal mine, located in Anshun city in Puding County, was being upgraded at the time of the explosion, the report said.

Five of the survivors remained hospitalized after being poisoned by carbon monoxide.

Earlier this week, a Chinese safety official, commenting on a spate of recent coal mine disasters, said lax enforcement of safety laws and poor equipment were partly to blame for making Chinese coal mines the most dangerous in the world.

Huang Yi, spokesman for the State Administration of Work Safety, said Chinese coal mines are poorly equipped to protect miners' lives. He said as much as one-third of the equipment at main state-owned mines needs to be replaced.

"Punishments specified by the laws are very harsh," sometimes running as high as $300,000, Huang told Beijing's Economic Observer. "But the problem is that enforcement of these laws is not strict" and no mine has been hit with the heaviest fines.

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