A powerful earthquake measuring 7.5 has hit China's southern province of Sichuan, shaking buildings as far away as Beijing, Shanghai and Bangkok.

It was not immediately clear if there were any casualties or damage from the tremor which the the US Geological Survey (UGS) earlier put at 7.8.

The epicentre of the quake was 93 kilometres north of Chengdu.

Wenchuan, which took full force of the quake, has a population of 111,000 people.

It is in an ethnic Tibetan area in Aba county which recently saw violent clashes between Tibetans and Chinese authorities.

According to some reports there was a second earthquake measuring 3.9 which hit the Beijing district of Tongzhou at roughly the same time.

Telephone lines in the affected area are jammed and there are still no reports of casualties.

Reports from Thailand say high buildings in Bangkok continued to shake several minutes after the tremors began.

"We felt continuous shaking for about two or three minutes. All the people in our office are rushing downstairs. We're still feeling slight tremblings," said an office worker in Chengdu.

China's tallest building, the Jinmao Tower, and other highrise buildings in Shanghai's financial district were evacuated after tremors were first felt.

"People were shouting 'get out, get out', so we all ran out of our dorm," said a student surnamed Zhang at a university in nearby Chongqing.

A spokesman for the China Earthquake Administration said it was still checking the epicentre and scale of the tremor.