The epicentre, with a depth of 7 km, was in Wuji Township, 21 kilometres away from the Yongshan County seat.
The shallow quake was strongly felt in the neighbouring counties of Suijiang, Daguan and Zhenxiong as well as the Zhaoyang District of Zhaotong City, which administers Yongshan, according to the provincial seismological bureau.
Nineteen people in Yongshan were injured and 1,424 houses were damaged, state-run Xinua News Agency reported.
Cracks have been spotted in adobe houses and more than 10 cattle lots collapsed at Jinping Village, according to the county government.
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About 50 km of roads, 41 km of tunnels and 21 km of power transmission lines were damaged in five townships.
More than 1,000 local officials, policemen and militia personnel are working in the affected regions in rescue efforts and disaster investigations.
About 200 firefighters from various cities have arrived in Yongshan for rescue operations.
Civil affairs authorities have sent 200 tents, 2,000 quilts and 2,000 coats to the county.
Twenty-two aftershocks had been reported so far.
Some houses were reported to have collapsed but communication in the county is unimpeded, according to the seismological bureau.
Over 600 people were killed more than 80,000 homes were destroyed in that quake.
The Yongshan earthquake is not an aftershock of the Ludian earthquake as the epicentres of the two quakes are 113 km away from each other, said Zhang Junwei, an official with the provincial seismological bureau.