Some of the 31 miners trapped in a north China mine flood still have a slim chance of survival, a safety official of the Inner Mongolia Autonomous Region said Thursday as rescue work went into its fourth day.

"Twelve of them are believed to be trapped at a mining platform 202 meters underground, at least 10 meters above the surface of the flood water," said Wu Qingfeng, a spokesman with the emergency rescue headquarters at Luotuoshan Coal Mine in Wuhai, a city about 600 kilometers from the regional capital, Hohhot.

The other 19 people believed to be at another platform 287 meters underground, might have drowned, he said.

Wu said it was not possible to use life detectors to see if people were still alive in the flooded pit. "Rescuers are still working all-out to drain the flood water and drill into the shaft."

On Wednesday, a group of People's Liberation Army (PLA) soldiers and excavators had drilled nearly 200 meters down.

"They will drill deeper Thursday and are expected to cap the hole where the water is pouring out, about 420 meters underground," said Wu.

An estimated 100,000 cubic meters of water poured into the pit of Luotuoshan Coal Mine following a flood Monday morning.

Of the 77 people working in the pit, one body has been recovered and 45 have survived the accident so far.

Most of the miners are migrants from Ningxia Hui Autonomous Region and the provinces of Shaanxi, Shanxi and Henan.