More than 500 people are reported to have been killed following a 6.9 magnitude earthquake in China's remote Qinghai province.
State media said at least 10,000 people were injured as houses, schools and offices collapsed.
The quake has also disrupted telecommunications, knocked out electricity and triggered landslides in the northwestern province.
There have already been at least 18 aftershocks and officials warn there could be many more.
The remote high-altitude region is prone to earthquakes and many of the casualties in the sparsely populated area were in Qinghai Province's ethnically Tibetan Yushu county.
Troops have been dispatched to the area to help search for survivors.
State agencies, as well as the Red Cross, are dispatching medical supplies and vitally needed tents to the area to assist with the operation.
Many survivors are sleeping outside in freezing conditions, either because their homes have been destroyed or they are too afraid to spend the night indoors.
'I see injured people everywhere. The biggest problem now is that we lack tents, we lack medical equipment, medicine and medical workers,' Zhuohuaxia, a local spokesman, told the Xinhua news agency.
The quake was centred in the mountains that divide Qinghai province from Tibet.
The foothills to the south and east of the area are home to herders and Tibetan monasteries of Yushu county, while the area to the north and west is arid and desolate.
The quake was centred 240km north-northwest of Qamdo in Tibet and 375km south-southeast of the mining town of Golmud in Qinghai, and had a depth of 10km, the US Geological Service said.