Miners guard the entrance of Machang coal mine in Guizhou province after a gas outburst killed 21 miners on Wednesday morning. [Photo/Xinhua]

GUIYANG - Twenty-one miners were killed and four others were missing in a coal and gas outburst Tuesday evening in a coal mine in Guizhou Province in southwest China, local authorities said early Wednesday.

The accident occurred at around 8:00 pm Tuesday at Machang Coal Mine, which belongs to Gemudi Company of Guizhou Water & Mining Group.

Eighty-three miners were working underground when the accident took place, and 58 of them managed to get to the ground safely.

Rescue operation is under way and the cause for the accident is under investigation.