The centre's advisor, Smith Thammasarot said that the quake was quite powerful and it may have after shock.

"I wish to warn that people should be careful as there could possibly be after shock following the earthquake," said Smith who was a former weather department chief.

Bangkok experienced tremors from earthquake that hit Laos and Thai-Burma border on Wednesday, sending many people running in panic out of many tall buildings in downtown areas.

Report from the US Geological Survey said that the earthquake, at about 6.1 Richer, struck western Laos near the border with Thailand and also along Thai-Burma border at about 3.57pm.

Many people in many small buildings in Sathorn, Silom, Sukhumwit, Phayatai and Vipavadi areas also felt the tremors. They reported building shaking.

The US survey said the quake was recorded at a depth of 33 kilometres in a region that is also close to the borders with China and Burma.

In Chiang Mai, residents of Mae Rim district became panic and rushed out the aged relatives outside their houses.

In Chiang Rai, residents of condominiums and hotel guests rushed out and waited outside.

The tremor also caused the tiered umbrella of Jomkitti Pagada to break and fall down.

Dr Penneung Wanitchai, an ecologist, said the layers of soft soil in Bangkok, magnified the tremor and the power was sent to high-rise building, and thus causing people on high-rise buildings to feel the quake.

He said it was quite frightening that the quake was felt in Bangkok although the epicenter was about 700 kms away. He said damages could happen if the quake happened within the 400 km radius of Bangkok.

Meanwhile Agence France Presse reported that the earthquake also sent people in Hanoi screaming for cover.

In the Vietnamese capital Hanoi, hundreds of people fled office towers and hotels when the city's tall buildings started to sway.

"I thought I was suffering a stroke or a heart attack -- then I realised it was an earthquake," said Fred Burke, a managing partner of the law firm Baker McKenzie, who was on the 13th floor of a Hanoi office building.

"The building shook for about a minute. The staff were screaming, and we told them to get away from the windows and take cover under the tables," said Burke, who comes from San Francisco.

The US Geological Survey estimated the tremor at a depth of 38 kilometres.

China's Seismological Monitoring Network, using a different scale, reported the quake at a strength of 6.6 while Thailand's meteorological department said a 4.7 magnitude aftershock hit at about 1005 GMT.

There was little information out of Laos as authorities tried to guage the impact of the quake in the sparsely populated, mountainous region.

A spokesman for the foreign ministry said tremors were felt in the town of Oudon Xay for 10 seconds. "People were afraid and they all left buildings."

 Authorities in the Chinese city of Jinghong, just over the border from the epicentre, said the quake was felt there but there were no reports of injuries or damage.