A villager walks his flock of sheep in the snow-covered Baishitou township of the Xinjiang Uygur autonomous region on Saturday.

URUMQI - At least three members of an earthquake research expedition team were pulled out of the mountainous Xinjiang-Tibet border region by airlift on Sunday after they became severely sick with high-altitude disease.

Local authorities required the team to end their research mission.

"A helicopter rescued them from the area where they were trapped," Hu Weihua, a senior official with the earthquake bureau of Northwest China's Xinjiang Uygur autonomous region, told China Daily on Sunday afternoon over the phone. The rescued team members will undergo medical examinations in southern Xinjiang's Hotan city, he added.

Since Aug 27, the 30-strong expedition team was on a one-month mission for earthquake and volcano research in the high-altitude areas of the Kunlun Mountain, according to a statement posted on the earthquake bureau's website on Saturday morning.

The team became stranded in an area about 5,000 meters above sea-level after it reported the breakdown of two provision vehicles loaded with fuels and food on Friday evening.

Song Heping, the team leader, called the local authorities in Hotan for emergency aid as one team member began to suffer from high-altitude disease, said the statement.

But the team ran into more danger two days later, as another five members showed symptoms of high-altitude sickness on Sunday morning.

Rescuers dispatched in vehicles from Hotan were hampered by hostile terrain and bad weather, according to another statement from the bureau on Sunday morning.

China National Radio reported that the area was hit by snowstorms, which made the rescue efforts difficult.

Song then requested airlift by the army to rescue the sickened team members. The research mission was forced to halt because of the loss of provisions and the team members' poor physical conditions, the statement said.

As of Sunday afternoon, at least three team members had been pulled out by airlift and the remaining members of the expedition team were waiting for the rescuers from Hotan, Xinhua News Agency reported.

But the Xinjiang meteorological station forecast on Sunday that the Kunlun Mountain area would continue to receive snowfalls in the coming two days, which could make the rescue operation more difficult.

Over the weekend, a wave of cold air blew into the regions of eastern Xinjiang and other northwestern provinces and autonomous regions including Qinghai, Gansu and Inner Mongolia, the National Meteorological Center said on Sunday.

In the northern part of the Hami prefecture in eastern Xinjiang, snowfalls were recorded on Saturday, leaving some crops damaged.

Early this week, much of North China will see temperature drops by 4 to 8 degrees, according to the National Meteorological Center.