copyright 2009, The Washington Post JAKARTA, Indonesia -- A powerful earthquake on the Indonesian island of Sumatra has left a once-vibrant port city heaped with corpses sealed in canary-yellow bags as soldiers and rescue workers searched for life early Friday beneath rubble entombing possibly thousands of people. Officials said at least 777 people died in a 7.6-magnitude quake Wednesday that flattened schools, shops and a hospital in Padang, a city of 900,000 on the west coast of Sumatra. They predicted that the death toll would rise. The quake also shook Singapore and Malaysia's capital, Kuala Lumpur. A second, less severe quake hit another part of Sumatra on Thursday. Often using little more than their bare hands, Padang residents labored through the night to find relatives and friends buried in the ruins. Sirens wailed as ambulances wound through wreckage-strewn streets and scattered fires flared from broken fuel lines, and power cuts and a shortage of medicine forced surgeons to halt operations in a hospital overflowing with gravely injured people. 'Let's be prepared for the worst,' Indonesia's president, Susilo Bambang Yudhoyono, said in Jakarta as he prepared to fly to Padang. A former general, he ordered the military to join rescue work in a city gripped by grief and fear. The disaster follows an unusual period of seismic turmoil around Sumatra that scientists say probably heralds a catastrophic quake on a scale not seen in the area since the early 19th century. Kerry Sieh, an American seismologist at Singapore's Nanyang Technological University, said Sumatra's current seismic spasms began in 2000 and have since produced about 30 quakes. Far worse is yet to come, he said, though not immediately. 'If you have a time-lapse picture of the Challenger space shuttle disaster -- the first thing you see is a little flame, a tear, and then the whole thing blows apart,' said Sieh, an authority on the area's geology and director of the Earth Observatory of Singapore. 'This is what is happening in Sumatra -- but in slow motion. The biggest explosion is yet to happen.' The Sumatra quakes do not appear to be directly connected to an earthquake roughly 6,000 miles away that triggered a tsunami Wednesday on the Pacific islands of Samoa, American Samoa and Tonga, scientists said. But Sumatra and the Pacific islands all lie within the 'Ring of Fire,' an arc of seismic turbulence noted for volcanic eruptions and earthquakes. Along a fault line that stretches from Burma to Australia, two tectonic plates meet and grind against each other. A rupture along this line caused the December 2004 Indian Ocean tsunami, in which about 230,000 people perished, many of them in the northern Sumatra region of Aceh. Earthquakes in and around Sumatra are 'becoming more frequent and of higher intensity,' said Haryadi Permana, a geologist at the Indonesian Science and Technology Agency. A massive quake is likely to occur in coming decades, he said, but 'it is impossible to predict when.' He said scientists have long warned that Padang and other towns were under threat, but 'the government never cared about that.' Some buildings in the city were reinforced before this week's disaster, but many still crumpled. Fearing more tremors, residents left their homes and prepared to sleep outside. Some hospitals have moved patients onto streets. Outside Padang's partially collapsed Jamil Hospital, at least 40 corpses were lying on the ground, Reuters news agency reported. Before flying to Padang on Thursday from Jakarta, Indonesia's health minister, Siti Fadilah Supari, said that thousands had probably died, but she added, 'We don't really know yet.' Sumatra is the center of Indonesia's oil and gas industry and home to endangered animals such as the Sumatran tiger and wild orangutan. Their habitat has been steadily reduced by illegal logging and the growth of Indonesia's powerful pulp and paper combines. Building regulations are often ignored, and Indonesia's relatively vibrant economy has left Padang and other towns on Sumatra with flimsy, hastily built structures. 