SHIZUISHAN, Ningxia: The death toll of Wednesday's coal mine explosion in northwest China's Ningxia Hui Autonomous Region has risen to 12, the local government said.

By 10:30 am, two people remained missing and seven were being treated at hospital -- one of whom suffered critical injuries, a workplace safety official said.

Wei said 22 workers were using dynamite to blast rocks in Dafeng Mine in Shizuishan when the blast happened at around 6:20 pm Wednesday.

Only one of them escaped without injury, he said.

Four workers died at the scene and four others died later at hospital.

By 10:30 am, rescuers had retrieved four more bodies.

Rescuers were searching for the two missing workers within a radius of 150 meters of the site, said Wei. "We have to be extra careful because experts have warned some dynamite did not explode."

He said the regional government had launched an investigation.

A similar tragedy was reported at the same mine in October last year, in which 16 people died and 48 were injured.

Dafeng Mine is owned by Shenhua Group, one of China's mining giants.