The quake, with a magnitude of 7.8, struck close to densely-populated areas of Sichuan province including the capital Chengdu.
It swayed buildings in Beijing and Shanghai and was also felt in Hong Kong, Hanoi and Taipei, residents said, and even in the Thai capital Bangkok, 1,800 kilometres (1,200 miles) from the epicentre.
Chinese Premier Wen Jiabao called it a "major disaster" and urged calm.
"Facing disaster, the most important thing is calm, confidence, courage and strong leadership," Wen told China's CCTV television on a flight to the heart of the quake-hit zone.
"We will definitely overcome this major disaster".
China's state-run Xinhua news agency cited local disaster relief officials saying 3,000 to 5,000 people were estimated to have died in just one district of Sichuan, Beichuan County.
A further 10,000 people were injured in the county, where officials said 80 percent of buildings had collapsed.
Xinhua earlier reported up to 900 students were feared buried