An earthquake measuring 7.5 rocked China's Sichuan province on Monday, less than 100 km (60 miles) from the provincial capital of Chengdu, the US Geological Survey said on its website.
It was not immediately clear if there were any casualties or damage from the tremor which the USGS earlier put at 7.8.
The tremor, centred 92 km northwest of Chengdu, was felt as far away as Beijing and Shanghai and the Thai capital Bangkok, where office buildings swayed with the impact.
"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.
In Beijing's financial district, many workers poured from their buildings but there were no visible signs of damage. The subway system was unaffected.
"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.
Sources said there was no immediate impact to the Three Gorges Dam project, the weight of whose massive reservoir, hundreds of km from Chengdu, experts have said could increase the risk of tremors.
A spokesman for the China Earthquake Administration said it was still checking the epicentre and scale of the tremor.