Jakarta, Indonesia-At least three people are dead in Sumatra as a result of an 8.4-magnitude earthquake that shook buildings across Indonesia and sparked widespread panic.
Residents and rescuers inspect a building destroyed by earthquake in Padang, Sumatra island.
One person was killed by a fallen tree in Bengkulu province and two died in Padang when the force of the quake damaged the building they were in, the social services department said.
The quake in the Indian Ocean shook buildings in Jakarta nearly 640 kilometers (400 miles) away from the epicenter off the coast of Sumatra and sent frightened people into the streets.
Closer to the epicenter, residents of Bengkulu province panicked and fled their homes, said John Aglionby, a reporter for the Financial Times, from Jakarta.
"The panic and concern is likely to continue for some time," he said. Many buildings along Sumatra's western coast collapsed, he added. The quake struck as the heavily Muslim country prepared for Islam's holy month of Ramadan, set to start in the coming days.
A small tsunami was detected in Padang, on Sumatra -- several hundred miles northeast of the epicenter -- according to the Pacific Tsunami Warning Center.
It measured about 60 cm (2 feet high), much smaller than the devastating tsunami that struck in 2004, the center said.
Indonesia's meteorological center said the small tsunami was not a concern and canceled its tsunami alert several hours after the quake struck, but it issued a new alert after a strong aftershock occurred at 9:40 p.m. (1440 GMT). The U.S. Geological Survey estimated the aftershock at 6.0.
Indonesia canceled its second alert about an hour and a half later.
A tsunami watch issued by the Pacific Tsunami Warning Center after the initial quake remains in effect for at least 24 countries around the Indian Ocean, including Australia, India, Sri Lanka, Malaysia, Pakistan, Iran, Yemen and Kenya.
Wednesday's quake was about 10 times smaller than the 9.0-magnitude temblor that caused the giant tsunami off the northern tip of Indonesia in 2004 that killed more than 200,000 people in seven countries rimming the Indian Ocean, John Applegate of the U.S. Geological Survey in Washington told CNN.
Wednesday's quake released 33 percent less energy, he added.
"The strongest shaking would have been in a relatively less populated area," Applegate said of Wednesday's quake.
The quake was strong enough, however, to be felt in Malaysia and Thailand. Several aftershocks have been recorded, including a 5.7-magnitude temblor about an hour later.
Applegate said Wednesday's quake was shallow, nearly 30 km deep, which is more of a threat to the local population, especially because it occurred beneath the sea.
"(With a) deep earthquake, the waves have to travel through a lot of the earth before they reach population; shallow earthquake means the local population is right there," he explained. "It also means that its more likely to rupture the surface, and with this being a subsea earthquake, that means there is the tsunami potential."
Several commercial skyscrapers in Jakarta were rocked by the quake, some 605 km southeast of the epicenter.
"It's pretty strong and people are being evacuated from the tall buildings," said Andy Saputra, CNN producer in Jakarta.
Although some employees were too afraid to leave their offices, companies ordered immediate emergency evacuations, he said. Workers exited structures via fire stairs and ran into the street, away from buildings and other potential dangers, Saputra added.
High-rise buildings also were evacuated in Singapore, 1,100 km northeast of the epicenter, CNN producer Martin Bohley said. He said he felt shaking for almost a minute.
Since the 2004 quake off Sumatra's northern tip, Applegate said earthquakes along Indonesia's coast have been moving south.
After the disastrous 9.0 quake that triggered the deadly tsunami nearly three years ago, the next major earthquake to strike the region was an 8.7 quake that struck close to the capital a year later.
John Aglionby, a reporter for the Financial Times, told CNN he was in his office on the 16th floor of a Jakarta high-rise when Wednesday's quake struck.
"I heard the blinds flapping in the window first, and then there was the chair shaking," he said. "It was quite spooky being up so high when it happened."
Aglionby said he ran into the street along with everyone else seeking safe haven. When he arrived on the street, the security guards and other people on ground level said they felt nothing.
"It's a bizarre experience of some people getting very scared and other people just continuing life as if nothing had happened."
Wednesday's quake struck near Bengkulu province which was devastated in June 2000 by a 7.9-magnitude earthquake -- followed by a 6.7-magnitude aftershock -- that killed more than 100 people, injured nearly 2,800 and damaged more than 40,000 buildings, according to the Red Cross.
Because of that experience, Aglionby said he was certain the residents of the sparsely populated region would not wait for a government warning to head for safer ground.
"As soon as they felt the land shaking they would run, and run fast uphill and on land," the journalist said.
Mark Ferdig, a spokesman for Mercy Corps in Banda Aceh, Indonesia, near where the 2004 quake hit, said the Indonesian government seemed better equipped to deal with this quake, because of its previous experiences.
"I think that the government is able to respond to events like this, whether it's quick enough and timely enough, we'll have to wait and see. But I'll have to say that the government has learned from the recent disasters."
Since the devastating tsunami of December 2004, Indonesia has fallen victim to 15 earthquakes with magnitudes of 6.3 or higher, according to the USGS. The quakes have killed almost 8,000 people, with the bulk of the deaths coming last summer.
The deadliest quake last summer came on May 26, 2006, when a magnitude-6.3 quake 10 miles south-southeast of Yogyakarta left 5,749 dead. On July 17, 2006, a magnitude-7.7 temblor hit 145 miles south-southwest of Tasikmalaya, in Indonesia's Java region. The quake killed 730 people.
Another devastating quake on March 28, 2005 -- a magnitude-8.7 about 125 miles west-northwest of Sibolga -- killed 1,313 people.