BANGKOK (AP) -- A strong earthquake shook a border area between northern Thailand and Laos early Thursday, swaying high-rises in Bangkok and Vietnam's capital.
Residents of Chiang Mai, northern Thailand's biggest city, felt prolonged shaking but saw no major damage.
Chiang Mai resident Petchnoi Osathaphan said the long shaking left her feeling dizzy. "There are three new cracks at the baseboards and close to the windows," she said of her house near the Mae Ping River.
High-rise buildings swayed slowly for half a minute in Bangkok, startling residents. Many online videos showed light fixtures swaying during the temblor.
Vibrations were also felt in Hanoi, Vietnam.
The U.S. Geological Survey said the 6.1 magnitude quake was about 10 kilometers (6 miles) below the surface.
It was centered just inside Xaignabouli province in Laos, some 31 kilometers (19 miles) from Chaloem Phra Kiat district in Thailand's Nan province, which is about 610 kilometers (380 miles) north of Bangkok.
Moderate quakes of 4.6 and 5.7 magnitude shook the same area overnight.
The Thai-owned, coal-fired Hongsa Thermal Power Plant in Xaignabouli said its system to prevent damage from tremors operated as planned and shut down the system to avoid damage. It said an initial survey of the plant's two dams showed no structural damage, but a more comprehensive survey was expected to be completed within 24 hours. Some structures suffered minor damage, it added.
Thai-owned CK Power said that according to preliminary inspections, two hydroelectric plants it operates in the area, the Xayaburi Hydroelectric Power Plant and the Nam Ngum 2 Hydroelectric Power Plant, suffered no damage from the quakes and continued to generate electricity for Thai and Laos state power authorities.