The U.S. Geological Survey measured the quake at magnitude-6.0. It struck shortly before 6:00 p.m. local time and the USGS said the epicenter was 30 miles northwest of Guangyuan town in Sichuan province at a depth of 6 miles.
Panicked residents fled into the streets as the quake rattled Qingchuan county in southwest Sichuan, and also jolted buildings in neighboring Shaanxi province's Hanzhong and Xi'an cities and the sprawling municipality of Chongqing, the official Xinhua News Agency reported.
The casualties were reported in Yaodu, a township in Qingchuan, Xinhua said.
The earthquake occurred a few hours after the Olympic torch relay passed through Sichuan's capital of Chengdu - its last stop before the flame officially opens the Beijing Games on Friday. There were no reports of the quake being felt in Chengdu.
The temblor was the latest of scores of aftershocks from the 7.9 quake that struck Sichuan on May 12, killing almost 70,000 people and leaving 5 million homeless.
On Friday, an aftershock with the same magnitude as Tuesday's hit Pingwu and Beichuan in Sichuan, injuring 231 people.