Chinese media say at least 67 people have died and others are trapped under rubble in Qinghai province after an earthquake said to be magnitude 6.9.
The quake struck at 0749 (2349 GMT) 380km (240 miles) south-south-east of the city of Golmud, at a depth of 10km, according to US Geological Survey data.
It appears that at least some of the deaths occurred in Qinghai's ethnic Tibetan town of Yushu.
The quake was followed by two tremors measuring 5.3 and 5.2.
"Soldiers have been dispatched to save the people buried in the collapsed houses," local official Huang Limin was quoted as saying by China's state news agency Xinhua.
"Certainly there have been people hurt," one resident told Reuters news agency.
"Rescuers are trying to pull them out. A lot of one-storey houses have collapsed. Taller buildings have held up, but there are big cracks in them."
People from the Yushu prefecture highway department were frantically trying to dig out colleagues trapped in a collapsed building, department official Ji Guodong told Reuters by telephone.
Zhuo De, an ethnic Tibetan resident of Yushu, who spoke by phone from the capital of Qinghai province, Xining, after contacting his family in Yushu, said dozens of people might have been hurt.
"The homes are built with thick walls and are strong, but if they collapsed they could hurt many people inside," he said.
AFP news agency notes that the remote high-altitude region is prone to earthquakes.
The region, which is home to ethnic Mongolians and Tibetan farmers and herdsmen, is dotted with coal, tin, lead and copper mines, it adds.