An aftershock measuring 5.1 on the Richter scale hit Wenchuan County in southwest China's Sichuan Province at 2:23 AM Thursday, according to the National Earthquake Network Center.

The quake struck an area 31.3 degrees north latitude and 103.3 degrees east longitude. It came from about 22 km underground.

No casualties have been reported.

Wenchuan was the epicenter of the May 12 earthquake last year that left more than 80,000 people dead or missing.

(Xinhua News Agency January 15, 2009)