The quake struck on the day the Olympic torch relay passed through the capital of the region, where almost 70,000 people were killed and 10 million displaced in the 8.0 earthquake in May. The Beijing Games begin on Friday.
Xinhua said five of the injured were in critical condition.
The quake struck the county of Qingchuan at 5:49 p.m. local time (9:49 GMT), with its epicenter 50 km (30 miles) northwest of Guangyuan town. Minor aftershocks were still being registered in the province.
The May 12 quake, which affected more than 47,000 villages, left some 1.4 million people in remote communities completely impoverished. China's direct economic losses from the earthquake have been put at more than 1 trillion yuan (around $150 billion).
