The quakes struck near the border of Yunnan and Guizhou provinces, the first one at 11:19am (0319 GMT) and the second one about 45 minutes later, the US Geological Survey (USGS) said.
About 150 people were injured and 20,000 homes were damaged, the official Xinhua news agency said.
Most of the victims were from Yiliang county, Yunnan province, near the epicentre of the quakes, which struck at a depth of 9 km (5.6 miles) according to the USGS. One person was reported to have been killed in nearby Zhaotong city.
By mid-afternoon, authorities had moved more than 100,000 from the area as a series of aftershocks struck. No deaths were reported in Guizhou province.
Buildings in China's less developed regions are often thrown up with little regard for construction standards, making them susceptible to earthquakes.
In 2008, about 87,600 people were killed in the southwestern Chinese province of Sichuan when a 7.8 magnitude earthquake hit.
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