Singaporeans experienced two rounds of tremors in the space of two hours on Tuesday, following two earthquakes in Padang, Indonesia.
Singapore's Meteorological Services Division said the first tremors were felt at about 11.50am after an earthquake measuring 6.6 on the Richter scale struck Padang on the island of Sumatra.
The epicentre was 50 kilometres north-northeast of Padang and some 430 kilometres south-west of Singapore.
The second round of tremors occurred around 1.50pm after another earthquake, also measuring 6.6 on the Richter scale, struck Padang.
The Police and the Singapore Civil Defence Force (SCDF) received nearly 1,000 calls from the public reporting tremors after the two quakes.
The tremors were felt in many parts of Singapore and in some 236 buildings.
Most of the buildings were in Ang Mo Kio, Yishun, Toa Payoh, Woodlands, Serangoon, Sengkang and CBD areas like Robinson Road and Shenton Way.
Callers to the MediaCorp News Hotline reported tremors were also felt at Beach Road and Choa Chu Kang.
Of those affected, 131 were HDB buildings, 95 commercial buildings and 10 private residences.
Witnesses said some tall buildings in the central business district swayed slightly.
Several buildings, like the Concourse, Capital Square and Centennial Tower in the city, and even Ngee Ann Polytechnic in Clementi, were evacuated.
Police said there were no reports of injuries from the tremors in Singapore.
Office worker Nicholas Wong said he and his colleagues were at their office shortly before lunchtime when they felt the building shaking.
"We grabbed our bags and just evacuated," he told 93.8 Live radio station.
"Everyone was panicking. One of my colleagues was crying because she had never felt such an effect before. We were all rushing out of the building."
But public relations executive Gavin Liow, 23, said he and his colleagues took it calmly.
"I thought, what the hell was it? You don't expect such things to happen," he told AFP.
Danny Tan Ming Xiong, 24, said he and his colleagues also felt the tremors.
"We were kind of freaked (the) first time. My colleagues and I thought we were giddy. Everyone started asking each other if we felt it, then realised the building was shaking," he told AFP.
"My company made the decision to get out of the building. We went down 40 storeys by stairs."
A spokesman for Saint Andrews Junior College said the first tremor disrupted lessons and students were dismissed after the second one "to pre-empt further interruptions, and in the students' interests and safety."
Another office worker told Channel NewsAsia he saw people screaming as they went out.
Others felt no tremors at all but got swept along by the general reaction.
"I didn't feel anything when one of my colleagues called me to evacuate," said South African Bulelwa Makina, 24.
"This is my first time feeling a tremor in Singapore but because I have been here for a while, I do know that Singapore does get tremors from other countries so I wasn't shocked," she told AFP.