Eighty professional rescuers are working to reach 12 miners trapped underground in a caved-in coal mine in Inner Mongolia Autonomous Region.

The accident happened around 3:10 a.m. Friday in Yuanlin Coal Mine in Xianghuang banner (county) of Xilin Gol league, which is about 350 km northeast of the autonomous regional capital city of Hohhot, according to the regional coal mine safety supervision bureau.

At the time of the accident, 13 miners were working underground. One miner escaped.

The 80 rescuers have been clearing the shaft from two mine entrances, but 20,000 cubic meters of collapsed rubble, mostly rocks, has complicated rescue efforts, the rescue headquarters said in a statement.

An initial investigation found that the mine's floor-to-roof pillars were "insufficient."

The cave-in is the latest in a series of coal-mine accidents in China recently.

On Nov. 10, an underground gas outburst in the southwestern province of Yunnan trapped 43 miners, of whom 35 have been confirmed dead while the other eight remain missing.

On Tuesday, another gas leak in a coal mine in the central province of Hubei killed six miners.?