The temblor Wednesday started fires, severed roads and cut off power and communications to Padang, a coastal city of 900,000 on Sumatra island. Thousands fled in panic, fearing a tsunami.
Buildings swayed hundreds of miles (kilometers) 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.
At least 500 buildings in Padang, the regional capital, collapsed or were badly damaged, said Disaster Management Agency spokesman Priyadi Kardono, adding that 200 bodies had been pulled from the rubble there.
The extent of damage in surrounding areas was still unclear due to poor communications, he said.
The magnitude 7.6 quake hit at 5:15 p.m. (1015 GMT, 6:15 a.m. EDT), 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 a dozen 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 shaking 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. At daybreak, residents 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."
Health Minister Siti Fadilah Supari told MetroTV that two hospitals and a mall collapsed in Padang.
"This is a high-scale disaster, Supari said.
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.
Rustam Pakaya, head of the Health Ministry's crisis center, said Wednesday that thousands of people had been trapped under the collapsed houses. It was unclear how many people were still missing or trapped by morning.
"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.
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 - spawned tsunami that killed more than 100 people. Experts said the seismic events were not related.
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Associated Press writers Ali Kotarumalos, Irwan Firdaus and Niniek Karmini contributed to this report.
