The aftershock jolted the area on Friday afternoon, leaving 231 people injured, four critically, a media report quoted China Earthquake Networks Centre and local government officials as saying.

The epicentre was located between Pingwu and Beichuan counties. The tremor caused severe landslides in the northern part of the province but no fatalities were reported.

The two counties were among the hardest hit by the May 12 earthquake. People rushed outside when they felt the aftershock, but most of them went back indoors once the tremor stopped, China Daily reported.

In Pingwu, 130,000 people were affected, 540 houses destroyed and 2,450 others damaged, Meng Xiancai, deputy head of the county's publicity department, said. Most of the communication facilities were damaged in 25 towns of Pingwu.

Yin Xianjin, a lawyer in Deyang, a city close to the epicentre, was on the first floor of a building when he started to feel it move.

"Luckily, the building stopped moving very soon," he said, adding it was one of the strongest aftershocks since May 12.