HOH XIL, Qinghai, Sept. 23 (Xinhua) -- Rescuers are racing to reach seven rangers trapped by a sudden blizzard since Saturday in the Hoh Xil National Nature Reserve on the Qinghai-Tibet Plateau.

The rangers used satellite phone to call the reserve's administrative bureau on Saturday and asked for rescue. They said their two vehicles were out of fuel and they could only hold out for three days with the remaining food.

The bureau immediately sent a group of eight wardens in three vehicles for the rescue. However, by Tuesday morning, the rescue vehicles were mired in snow-swamped ground some 40 km away from the trapped rangers.

Dubbed "No man's land", the Hoh Xil mountain steeples more than 5,000 meters above sea level. The group of rangers went out for patrol work on Sept. 11. Some of them are suffering from altitude sickness. Their conditions are thought to be critical.

The bureau plans to send more people to aid the rescue.

Established in 1998, the Hoh Xil National Nature Reserve has helped rehabilitate the population of endangered Tibetan antelopes, thanks to rangers' work to combat poaching.

The number of Tibetan antelopes in or near the reserve has increased to 35,000 from about 20,000 in 1998.