LANZHOU - The death toll in Tuesday's avalanche in Northwest China's Gansu province has risen to four. Rescuers are still searching in snow-packed debris for six other missing prospecting workers Thursday morning.

The avalanche occurred late Tuesday night in a remote part of Subei county, burying the campsite of the Heicigou Antimony Ore Prospecting Station.

Hu Jianzhong, head of the station, said there were a total of 21 people at the campsite at the time of the avalanche. Ten people were buried, and 11 others managed to escape.

Rescuers have sent one severely injured survivor to hospital, Hu said.

Rescuers are still double-checking the number of workers who may have stayed at the campsite.

Heicigou, situated over 4,300 meters above sea level, is located 180 km away from the county seat of Subei, which is a dense Mongolian ethnic area.

Since Monday, the area had been hit by heavy rainstorms rarely seen in the local history, and the local observatory said precipitation exceeded 500 millimeters in the 23 hours prior to 3 pm Tuesday.

A heavy snowfall hit the mountainous region on Wednesday, which further aggravated the condition of the rescue work. By Thursday, snow on ground reached 60cm deep. Rescuers could only reach the avalanche site on foot.

The prospecting team is owned by Subei Jinze Mining Co Ltd. The share-holding company has prospecting rights on a 1,600-square-km area in Subei.