A disaster management official says at least 200 people have been killed by the powerful earthquake that struck western Indonesia.
Priyadi Kardono, a spokesman for the National Disaster Management Agency, says the deaths were counted in the coastal Sumatran city of Padang, following Wednesday's 7.6 magnitude quake.
A higher death toll is expected once officials tally casualties in other areas of West Sumatra province where communications and roads have been severed.
The U.S. Geological Survey said another powerful earthquake struck western Indonesia at 8:52 a.m. local time Thursday on Sumatra Island, about 180 miles away from the more powerful quake Wednesday. There were no immediate reports of damage from the 6.9 magnitude quake.
Kardono said Thursday that about 500 buildings collapsed in Padang - a sprawling regional capital of 900,000 people.
Buildings swayed hundreds of miles away in neighboring Malaysia and Singapore.
In the sprawling low-lying city of Padang, the shaking was so intense that people crouched or sat on the street to avoid falling. Children screamed as an exodus of thousands tried to get away from the coast in cars and motorbikes, honking horns.
Authorities say untold numbers of houses, hotels, schools and shops have crumbled to the ground, reports CBS News correspondent Celia Hatton.
"What we're hearing from Padang is sporadic," Sean Granville-Ross of Mercy Corps told Hatton. "It's difficult, communications are down. What we have heard is this was a huge earthquake and there has been significant damage. There are obviously large numbers dead and injured, and we're expecting those to increase as daylight breaks."
The magnitude 7.6 quake hit at 5:15 p.m., just off the coast of Padang, the U.S. Geological Survey reported. It occurred a day after a killer tsunami hit islands in the South Pacific and was along the same fault line that spawned the 2004 Asian tsunami that killed 230,000 people in 11 nations.
A tsunami warning was issued Wednesday for countries along the Indian Ocean, but was lifted after about an hour; there were no reports of giant waves.
The temblor flattened buildings and felled trees in Padang, damaged mosques and hotels and crushed cars. A foot could be seen sticking out from one pile of rubble. In the gathering darkness shortly after the quake, residents fought some fires with buckets of water and used their bare hands to search for survivors, pulling at the wreckage and tossing it away piece by piece.
"People ran to high ground. Houses and buildings were badly damaged," said Kasmiati, who lives on the coast near the quake's epicenter.
"I was outside, so I am safe, but my children at home were injured," she said before her cell phone went dead. Like many Indonesians, she uses one name.
The loss of telephone service deepened the worries of those outside the stricken area.
"I want to know what happened to my sister and her husband," said Fitra Jaya, who owns a house in downtown Padang and was in Jakarta when the quake hit. "I tried to call my family there, but I could not reach anyone at all."
Initial reports received by the government said 75 people were killed, but the real number is "definitely higher," Vice President Jusuf Kalla told reporters in the capital, Jakarta. "It's hard to tell because there is heavy rain and a blackout," he said.
Health Minister Siti Fadilah Supari told MetroTV that two hospitals and a mall collapsed in Padang.
"This is a high-scale disaster, more powerful than the earthquake in Yogyakarta in 2006 when more than 3,000 people died," Supari said, referring to a major city on the main Indonesian island of Java.
Hospitals struggled to treat the injured as their relatives hovered nearby.
Indonesia's government announced $10 million in emergency response aid and medical teams and military planes were being dispatched to set up field hospitals and distribute tents, medicine and food rations. Members of the Cabinet were preparing for the possibility of thousands of deaths.
"There will be challenges primarily to get aid into the city," Granville-Ross told Hatton. "We'll have to look at air, land. The other neighboring provinces are 10 hours by road."
Rustam Pakaya, head of the Health Ministry's crisis center, said "thousands of people are trapped under the collapsed houses."
"Many buildings are badly damaged, including hotels and mosques," said Wandono, an official at the Meteorology and Geophysics Agency in Jakarta, citing reports from residents.
Kalla said the worst-affected area was Pariaman, a coastal town about 40 miles northwest of Padang. He gave no details on destruction or deaths there.
Local television reported more than two dozen landslides. Some blocked roads, causing miles-long traffic jams of cars and trucks.
On Tuesday, a powerful earthquake off the South Pacific islands of Samoa, American Samoa and Tonga - thousands of miles (kilometers) from Indonesia - . Experts said the seismic events were not related.
View photos of the tsunami aftermath in Samoa
Both Indonesia's Aceh province, which was devastated in the 2004 tsunami with 130,000 dead, and Padang lie along the same fault. It runs the along the west coast of Sumatra and is the meeting point of the Eurasian and Pacific tectonic plates, which have been pushing against each other for millions of years, causing huge stress to build up.
Scientists have long suggested Padang would suffer a similar fate to Aceh in the coming decades. Some predictions said 60,000 people would be killed - mostly by giant waves generated by an undersea quake.
The dire predictions spread alarm across Padang, which was struck by an earthquake in 2007 that killed dozens of people.
Indonesia, a vast archipelago with more than 17,000 islands and a population of 235 million, straddles continental plates and is prone to seismic activity along what is known as the Pacific Ring of Fire.