The quake struck at the shallow depth of 10 kilometres (6.3 miles) at 9.49 pm (1349 GMT), the US Geological Survey (USGS) said, in a region that lies close to China's borders with Myanmar and Laos.

China's official Xinhua news agency said at least one person had been killed and 38 others injured, eight of them critically, with thousands of homes damaged.

"Many houses collapsed and we are investigating the casualties," a local official told the agency. "The aftershocks seem non-stopping."

Provincial officials declared a top-level emergency, with 3,200 troops dispatched in a "race to save more lives", according to Xinhua.

An additional 600 professional rescuers with sniffer dogs have been sent to the quake zone.

The epicentre was located in Jinggu County, 85-kilometres from Pu'er city, in a region famous for its tea plantations. The quake was also felt in Yunnan's provincial capital Kunming.

Xinhua gave a significantly higher reading of 6.6-magnitude, citing the China Earthquake Networks Center.

The agency said buildings shook for several seconds, while some towns in the area had lost power supply and telecommunications.

"The whole building was shaking terribly with a loud cracking sound. Plates fell off in the kitchen. We all ran out and the streets now are packed with people," Ms Li Anqin, a woman living in Weiyuan town, the county seat of Jinggu, told Xinhua via telephone.

Some 4,700 homes were damaged in the neighbouring city of Lincang, according to the news agency.

Photos on social media showed damaged houses, cracked walls and fallen roof tiles, and crowds of people gathered outside into the night.

The epicentre of the quake was in a densely-populated but underdeveloped area home to various ethnic minorities, according to Xinhua.

Yunnan is acutely vulnerable to earthquakes. The region sees frequent seismic activity from the collision of the Indian and Eurasian tectonic plates, which form the vast Himalaya mountain range.

In August, a 6.1-magnitude struck Yunnan killing more than 600 people. More than 3,000 people were injured, while more than 80,000 homes were fully or partially destroyed.

Rescuers arriving on the scene early October 8 said the destruction did not initially appear to be on the massive scale of the August quake.

"It's not like last time in Ludian -- there are no massive collapse of buildings. It's such a relief," rescue chief Chen Xianhe told Xinhua.

Yunnan's neighbouring Sichuan province was struck by a particularly brutal quake in 2008 in which more than 80,000 victims perished.