High altitudes, rugged terrain and limited logistics support in the quake-hit Yushu prefecture of China's northwestern Qinghai Province have made rescue and relief work difficult, an official said Thursday.

Many rescuers working in the quake zones were suffering from altitude sickness, Miao Chonggang, deputy head of the China Earthquake Administration's quake relief and emergency response department, told a press conference.

Yushu prefecture sits at about 4,000 meters above sea level.

The altitude sickness even affected the sniffer dogs brought along by the rescuers, making them less efficient in the search for survivors, Miao said.

He said the complex terrain in the quake zone, which lay along deep canyons, also complicated rescuers' access, and local logistics support was "very limited."

"Many rescue teams do not have sufficient space to camp or supplement supplies of instant food," Miao said. "Not to mention the high altitude and the cold. As you know, it is still winter in the quake zone."

The 7.1-magnitude quake had also destroyed electricity and communication lines in Yushu Tibetan Autonomous Prefecture, and brought down most of the wood-brick buildings, said Miao.

At least 617 people were killed, more than 9,000 were injured and 313 were missing after a 7.1-magnitude earthquake jolted Yushu early Wednesday.

(Xinhua News Agency April 15, 2010)