A gas blast at a coal mine in southern China killed 11 people and injured nine, the government said Thursday.

The explosion occurred Wednesday at the Aotian Coal Mine in Sichuan province when 28 miners were working underground, the official Xinhua News Agency said. The cause of the blast was under investigation, it said.

Thousands of workers are killed each year in China's mines, the world's deadliest. Fires, floods and explosions occur almost daily despite repeated safety crackdowns, mostly due to poor equipment and lax enforcement of safety rules.