The quake hit at 1:13 am local time (2243 IST) at a depth of just 10 kilometres, USGS said.
Its epicentre was in Menyuan county, around 100 kilometres from the city of Jinchang, according to state media and USGS.
China's Earthquake Networks Center put the magnitude higher at 6.4, according to state news agency Xinhua.
China is regularly hit by earthquakes, but more regularly in its southwestern provinces of Sichuan and Yunnan.
In October 2014, hundreds of people were injured and more than 100,000 displaced after a shallow 6.0 magnitude tremor hit Yunnan province, close to China's borders with Myanmar and Laos.