The quake, initially reported as a magnitude 6.7, struck at 6:34 a.m. on Saturday (2234 GMT on Friday) at a shallow depth of 6.2 miles (10 km) on the Tibetan Plateau, the USGS said.
The quake struck in the Nyingchi region of Tibet. The Nyingchi government said in a statement on its microblog that the quake's epicentre was in an uninhabited region and that it had yet to receive any casualty reports.
The epicentre was within 150 miles (240 km) of the Indian towns of Along, Pasighat and Tezu, the USGS added.
A magnitude 6.3 quake is considered strong and is capable of causing severe damage.
Southwestern parts of China are frequently hit by earthquakes. A huge quake in Sichuan province in 2008 killed almost 70,000 people.