In Beichuan county, just east of the epicenter, up to 5,000 people were killed and 80 per cent of buildings collapsed, Xinhua said. Another 10,000 people were injured.
Prime Minister Wen Jiabao described the quake, which measured 7.8 on the Richter scale, as a "major disaster" and appealed for calm.
Rescuers are battling to free 900 students buried beneath their high school in the city of Dujiangyan, in Sichuan. It is not clear how many survived the collapse of the three-storey building.