Rescuers are working through the rubble to find survivors after a magnitude 6.9 earthquake hit the mountainous Qinghai province of China, killing at least 400 people.
Reports said around 10,000 others have been injured, with the earthquake burying many more in northwestern China, reports and government agents said.
Many houses collapsed, roads have been damaged or blocked by landslides and telecommunications have been disrupted, local officials said after the quake.
"The injured are everywhere in the street, a lot of people are bleeding from head wounds," Xinhua quoted another local official, identified as Zhuohuaxia, as saying from the town of Jiegu.
Soldiers dispatched, rush to rescue begins
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"Soldiers have been dispatched to save the people buried in the collapsed houses," the official Xinhua news agency quoted a local official, Huang Limin, as saying.
The quake wreaked havoc on the flimsy earth and wood houses near the epicentre - a high-altitude area near the border with Tibet and at least 12 hours by road from the provincial capital.
But some sturdier concrete structures also were toppled, according to images broadcast by state television.
Among the casualties were children trapped under the rubble of at least one collapsed school in the town, seat of the Yushu government and near the quake's epicentre, with Xinhua reporting at least five students had died.
"There are about 20 children buried in the debris," Kang Zifu, a local fire department official, was quoted as telling state television.
"We're hurrying to help them... We're also working on the Jiegu commerce and industry department office, where there are about 40 to 50 people buried. They are alive, and we've had contact with them
Cracks appear in large dam
The USGS said the quake hit at 7.49am (0949 AEST) and was centred 380km south-southeast of the city of Golmud, at a depth of 46km.
Three aftershocks rattled the area shortly after the quake, with magnitudes of up to 5.8, the USGS reported.
Experts reported that the quake caused cracks in a local dam.
Earlier, calls by AFP to local government headquarters and businesses in Yushu county, the quake's epicentre, went unanswered as the earthquake administration said the quake caused disruptions to telecommunications in the area.
The county has a population of about 80,000 people.
Xinhua quoted officials saying rescue personnel and equipment were being rushed to the area but warned they could be hampered as roads had been damaged or blocked by landslides.
The remote high-altitude region is prone to earthquakes.
The zone, which is home to ethnic Mongolians and Tibetan farmers and herdsmen, is dotted with coal, tin, lead and copper mines.
A 6.2-magnitude quake rattled Golmud in August last year, triggering landslides and the collapse of about 30 homes, but there were no reports of casualties.
A massive 8.0-magnitude quake in May 2008 in neighbouring Sichuan province devastated a huge area of southwestern China, leaving at least 87,000 people dead or missing.
