Residents in parts of Singapore said they felt tremors lasting up to a minute yesterday, around the same time that a magnitude-6.5 earthquake struck the Indonesian island of Sumatra.
Ms Jamilah Ismail, who lives on the 25th floor in Marine Crescent, said she was reading a newspaper when she felt giddy and noticed that her bedroom door was rattling. "The cord dangling from the ceiling fan was also swaying," she said.
Civil servant W. Ong, who lives in Sengkang, said she was about to get out of bed when she felt it move. "That was just before 7am. It happened a few more times but the tremors were not as strong as the first jolt."
Fellow Sengkang resident Krish Srikanth said: "I felt as if my head was spinning. The table was shaking for a few seconds. My family members felt it too."
Indonesia's Meteorological, Climatological and Geophysical Agency said the earthquake struck at about 5.56am there, or 6.56am in Singapore.
A Singapore Civil Defence Force spokesman said it did not receive any calls requesting immediate assistance.
Explaining why tremors were felt in Singapore, Assistant Professor Wei Shengji from the Earth Observatory of Singapore said yesterday's quake was an intra-plate quake, which occurs in the interior of a tectonic plate.
Such earthquakes usually produce stronger high-frequency shaking than those that take place at a plate boundary.
"This is because of the difference in friction properties, which allows intra-plate quakes to release greater amounts of energy," he said.
On March 2, Singaporeans living in Jurong and Punggol felt tremors when Sumatra was rocked by a powerful magnitude-7.8 earthquake.
In September 2007, tremors from a magnitude-8.4 earthquake in Sumatra sent people in Singapore fleeing from their high-rise offices and apartments in Marine Parade, Punggol, Serangoon and the Central Business District.
Those who are indoors when they feel quake tremors should take cover under a table and keep away from items made of glass or any hanging objects, the police said.
They also advised residents not to take the lift or to use any naked light, in case there is a gas leak. Those who are outdoors should stay away from buildings and overhead electrical cables.