More than 20,000 houses were either damaged or had collapsed in the quake, which hit the border area of Yiliang county in Yunnan and Weining county of the neighbouring Guizhou province at 11:19 am local time, the official media reported.
The depth of its epicentre was about 14 km at 27.5 degrees north latitude and 104.0 degrees east longitude.
The quake left 43 people dead and 150 others injured, the state media said. All the victims were from Yiliang county. The epicentre was about 15 kilometres from the county seat of Yiliang.
As of 1 pm local time, the area had been struck by 16 aftershocks following the 5.7 magnitude quake, with the strongest one measuring 5.6 on the Richter Scale, the provincial seismological bureau said.
The province has sent work teams to the quake-hit area and the civil affairs department is transporting thousands of tents, quilts and coats to the affected region.
So far, no casualties had been reported from Guizhou province, but the quake had also damaged or even toppled homes in Weining county, said Chen Bo, head of the county government.