China said it had dispatched thousands of armed police, soldiers and firefighters to the scene. Premier Li Keqiang visited the town on Monday, Xinhua said, urging a quick rescue for those missing and trapped by debris.

The quake, in a remote part of Yunnan province, caused thousands of buildings, including schools to collapse, the official Xinhua news agency reported

The epicenter of the quake was Longtoushan town in the province's mountainous Ludian county.

Earthquakes frequently strike in the region. A quake in Sichuan province, also in the southwest, in 2008 killed almost 70,000 people.

The earthquake was the most severe in the region in a century, Xinhua said.