At least 200 trained rescuers were forced to leave a remote mountainous quake zone in northwest China after they exhibited signs of altitude sickness, local officials said Saturday.

The sick rescuers -- composed of para-military soldiers and firefighters from two coastal provinces -- had been evacuated from the quake-devastated Yushu county at dawn Saturday, said Li Pengxin, a senior provincial official who overseas the rescue operations.

Yushu, where a 7.1-magnitude earthquake struck early Wednesday, sits at about 4,000 meters above sea level. The high altitude, thin air, freezing temperatures and electricity shortages hampered the rescue operations.

Li said the evacuated rescuers were "seriously sick". Many felt dizzy, hard to breathe, and their lips turned dark purple. Some soldiers vomited continuously and others even spit blood.

Latest official death toll of the earthquake has climbed to 1,144. More than 80 percent of the houses, mostly made of mudbricks and wood, had collapsed.

Since Wednesday, thousands of professional rescuers, soldiers, police, fire-fighters and medical workers have been mobilized nationwide for the rescue operation. But rescuers and sniffer dogs particularly had to fight altitude sickness and rough weather in this mountainous region.

Thousands of survivors had been pulled out from the rubble in the last three days, the rescue authorities said, but more than 400 people remain missing.