More than 730 people were injured after the quakes hit Yunnan and Guizhou provinces on Friday, state media say.
The tremors struck mostly mountainous areas, causing landslides that blocked some roads.
The US Geological Survey registered the two strongest of the quakes at 5.6 magnitude.
Premier Wen Jiabao is expected to arrive in the area shortly.
China's Xinhua news agency quoted officials in Yunnan as saying 6,650 houses had been destroyed in the province and 430,000 others damaged.
More than 100,000 people have already been evacuated, said Xinhua, and the Red Cross has sent 650 tents and 3,000 quilts to the region.
The authorities have deployed the army to assist rescue teams in the rough terrain.
"Roads are blocked and rescuers have to climb the mountains to reach hard-hit villages," Li Fuchun, head of Yunnan's Luozehe town, was quoted as saying.
Mobile and regular phone service in the area was experiencing disruption, according to reports.