Indonesia's Sumatra island was pounded by aftershocks on Thursday after the world's most powerful earthquake so far this year killed at least six people and buried many more under buildings.
Tsunami warnings were repeatedly issued and lifted for Indian Ocean rim countries after the latest tremors, which the U.S. Geological Survey (USGS) said took to a total of 19 -- ranging from magnitudes of 4.9 to 8.4 -- over the past 18 hours.
"We can expect aftershocks to continue for some time," USGS Geophysicist Dale Grant told Reuters.
The mayor of Padang, the capital of West Sumatra, said many people were trapped under collapsed buildings, and there were also reports of hundreds injured in Bengkulu to the south.
Padang was thrown into chaos after the initial 8.4-magnitude quake on Wednesday night, the strongest recorded across the globe this year, and many people fled in terror as daylight brought more tremors. Huge traffic jams were reported in the city.
"My family and neighbors are evacuating to higher ground. Everyone in the place where I live decided to evacuate," said 35-year-old Padang resident Eri Kamra. "I saw buildings collapse and one person lost consciousness after the morning quake."
A Reuters witness said that a four-story car showroom had collapsed, trapping several staff.
Part of Padang's main hospital also collapsed, and some injured people had to be moved out of wards to the relative safety of tents. "Many are still trapped underneath the rubble from last night's quake," Padang Mayor Fauzi Bahar told Reuters.
Officials were also deeply concerned about the situation in Bengkulu, a coastal city of about 300,000 people and the closest major town to the epicenter of Wednesday's huge quake.
Metro TV reported hundreds hurt there, though it was not possible to verify this as communications to the area were cut.
"The North Bengkulu area has been identified as the worst hit with half the area destroyed," said Rustam Pakaya, head of the health ministry's crisis centre in Jakarta. "Many hospitals, houses, government buildings and clinics have been destroyed."
The crisis center's latest casualty figures showed that six people had been killed and 40 injured by the quakes, some of which were felt in neighboring Singapore, Thailand and Malaysia.
"There is no explanation about why there are so many quakes hitting Indonesia at this time but Indonesia is perhaps the most active earthquake area in the world," Geophysicist Grant told Reuters.
Indonesia suffers frequent quakes, as it lies on an active seismic belt on part of the so-called Pacific "Ring of Fire". A huge earthquake measuring more than 9 struck the same area of Indonesia on Dec. 26, 2004, causing a massive tsunami and over 230,000 deaths in countries
across the Indian Ocean region.
Many people chose to sleep out in the open on Wednesday night rather than return indoors, said a Red Cross official in Bengkulu, a mountainous area that attracts few foreign tourists.
Bakri Beck, deputy for relief efforts at the National Coordinating Body for Disaster Management, said a team of ministers was leaving for Bengkulu.
They would take with them a medical team, a ton of medications, baby formula, tents and body bags, he added.
"Relief efforts are being hampered by the continuous occurrence of quakes along the west coast of Sumatra, which has resulted in power outages and disruption of communication," he said.