GUIYANG/HARBIN - Search and rescue efforts continued Wednesday for 22 miners who were trapped in two separate colliery disasters in China.

As of 10 am, four miners remained missing in a pit of Southwest China's Guizhou province, where an outburst of coal and gas killed 21 people Tuesday night.

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

Eighty-three miners were working in the pit, with 58 escaping.

Jiang Liangquan, head of the rescue team, said the bodies of the 21 who died had been retrieved. "The missing four are probably buried under rocks."

He said rescue efforts were difficult as the toxic gas density in the shaft remained high.

The mine reports an annual output of 450,000 tonnes.

Meanwhile, search and rescue efforts are still ongoing for 18 miners who remain trapped in a mud-rock flow accident that happened Monday in Heilongjiang province in northeastern China.

The accident was reported at 2:30 pm at a shaft of the Zhenxing Coal Mine in Hegang city. It trapped 25 people and only seven of them have been saved.