Residents survey the damage Thursday caused by an Indonesian earthquake. A second powerful quake rocked the western portion of the nation today. Initial numbers show more than 500 people are dead and that toll is expected to rise. Many more people are believed trapped in rubble as hundreds of buildings were damaged.

PADANG, Indonesia — Rescue workers used excavators today to pull out victims, some screaming in pain, from the heavy rubble of buildings felled by a powerful earthquake that killed at least 531 people. The death toll was expected to rise.

The brunt of Wednesday's 7.6-magnitude earthquake, which originated in the sea off Sumatra island, appeared to have been borne by Padang town where 376 people were killed. Four other districts accounted for the remaining deaths.

The region was jolted by another powerful earthquake this morning, causing damage but no reported fatalities.

More than 500 buildings including hotels, schools, hospitals and a mall were destroyed or damaged in Padang. Thousands of people were believed to be trapped in the rubble.

Padang's state-run Djamil Hospital was overwhelmed by the influx of victims and families. Dozens of injured people were being treated under tents outside the hospital, which was itself partly damaged.

"Let's not underestimate (the disaster). Let's be prepared for the worst. We will do everything we can to help the victims," President Susilo Bambang Yudhoyono said in Jakarta before flying to Padang, a coastal city of 900,000 and capital of West Sumatra province.

A total of 531 people were confirmed dead and 440 were seriously injured, the Social Affairs Ministry's crisis center said. Thousands were believed trapped, said Rustam Pakaya, head of the Health Ministry's crisis center.

One focus for emergency workers was a collapsed 4-story concrete building in downtown Padang, where 30 children had been taking classes when the quake struck. Four students were found alive and six bodies were dug from the rubble. Parents of missing students stayed up all night, waiting for signs of life.

The president ordered the military to deploy emergency response teams from Jakarta, West Sumatra and North Sumatra provinces. He said the military will provide earth-moving equipment to clear the rubble.

SurfAid, a New Zealand-based medical aid group, said its program director David Lange narrowly escaped death when he fled the Ambacang Hotel minutes before it collapsed.

"People are trapped and screaming for help but they are below huge slabs which will take heavy equipment to move," Lange was quoted as saying in a statement by SurfAid.

"I saw dozens of the biggest buildings collapsed in town. Most of the damage is concentrated in the commercial center market, which was fully packed," he said. At least 80 people were missing at the five-story Ambacang Hotel, said Indra, a paramedic who uses only one name.

The U.S. Geological Survey said the quake hit about 150 miles south of Padang. It damaged 1,100 buildings, including mosques and homes, in the town of Jambi, according to Mayor Hasfiah who uses only one name like many Indonesians.