The quake hit at 9:22 am (0122 GMT) in a sparsely populated area about 150 kilometres (100 miles) northeast of the major Qinghai city of Golmud, the US Geological Survey said.

The quake occurred at a relatively shallow depth of just 10 kilometres, the USGS said, adding that a 5.0-magnitude aftershock rattled the region two and a half hours later.

China's official Xinhua news agency said there were no immediate reports of casualties.

In Golmud -- an industrial city that is the starting point for the railway to Tibet -- people ran out of buildings as the quake struck, Xinhua reported.

"Some residents said it was the biggest tremor they had felt" since a quake measured at 7.8 jolted the area in November 2001, Golmud official Luo Zhenggang was quoted as saying.

The Qinghai-Tibet railway was largely unaffected by the earthquake, the railway said.

"Railway operation remains normal," a company spokesman told Xinhua. "But we have tightened safety surveillance along the route, and equipped every train with additional mechanical engineers."

Residents were shaken by the quake in the provincial capital Xining, more than 615 kilometres from the epicentre.

"So far there has been no damage reported in Xining city," an official at the city's seismology bureau named Zhang told AFP. "Residents living on higher floors generally reported feeling the tremor."

The quake also shook buildings more than 245 kilometres away in the city of Delinha, residents there said.

"It felt like a strong earthquake. Windows and doors shook. But it's calm now. The buildings here are undamaged," an official in Delinha told AFP on condition of anonymity because she was not allowed to talk to reporters.

The quake toppled a few ramshackle huts and walls of some mud houses were cracked near the epicentre, Xinhua quoted Gu Xiaodong, a senior district official, as saying. He said schools had also been closed.

"No casualties have been reported as yet," Gu said.

The epicentre was close to two coal mines, he said, adding: "But no serious damage has been incurred to the mine facilities so far."

China suffers frequent earthquakes. An 8.0-magnitude quake which hit the southwest province of Sichuan on May 12 flattened entire towns and left more than 87,000 people dead or missing.

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