The second powerful earthquake in as many days shook western Indonesia Thursday, collapsing buildings in a coastal city and triggering tsunami alerts around the region.

At least nine people were killed and 49 injured in the twin tremors, which caused tall buildings to sway in at least three countries.

On Wednesday, an 8.4-magnitude earthquake shook Southeast Asia. That tremor triggered a small non-destructive tsunami off the coastal city of Padang on Sumatra, the Indonesian island ravaged by the 2004 tsunami disaster. A tsunami warning was issued for wide areas of the region and nations as far away as Africa.

Thursday's magnitude-7.8 quake rattled the same area of Sumatra and caused extensive damage in Padang.

"Many buildings collapsed after this morning's quake," Fauzi Bahar, the mayor, told El Shinta radio. "We're still trying to find out about victims."

Thousands of frightened people piled in trucks or sought shelter on high ground.

Rafael Abreu, a geologist with the U.S. Geological Survey in Colorado, said Thursday's quake did not appear to be an aftershock to the temblor the day before. But the centers of both were close together.

"We are not calling it an aftershock at this point. It's fairly large itself. It seems to be a different earthquake," Abreu said.

"The quake seems to be pretty shallow," he said. "These are the quakes that can produce tsunamis."

Indonesia issued a tsunami warning, lifted it and then reissued it. Australia's Bureau of Meteorology issued a warning that unusual waves could hit Christmas Island early Thursday, but locals said there was no sign of a tsunami about an hour after the predicted time.

"The danger has passed," said Linda Cash, a manager at the Christmas Island Visitors Center. "There was no wave or damage or anything."

However, Cash said police were out early Thursday warning people to stay away from the beaches.

The USGS said the new quake was centered about 125 miles from Bengkulu, a city on Sumatra. It occurred at a shallow depth of about six miles and struck at 6:49 a.m.

The Pacific Tsunami Warning Center in Hawaii warned Thursday's quake had the potential to generate a destructive regional tsunami along coasts within 600 miles of the epicenter. It advised authorities to take immediate action to evacuate coastal areas.

After Wednesday's quake, frightened people fled their homes and ran inland, fearing a repeat of the 2004 earthquake and tsunami off the coast of Sumatra that struck a dozen nations around the Indian Ocean. That disaster killing an estimated 230,000 people in a dozen nations, most of them in Aceh province on Sumatra.

"Everyone is running out of their houses in every direction," Wati Said reported by cell phone from Bengkulu, a town 80 miles from the quake's epicenter. "We think our neighborhood is high enough. God willing, if the water comes, it will not touch us here. ... Everyone is afraid."

One witness, Budi Darmawan, said a three-story building near his office fell.

"I saw it with my own eyes," he told El Shinta radio.

Telephone lines and electricity were disrupted across a large swath of Indonesia, making it difficult to get information about damage and casualties.

Death tolls released by several agencies ranged from five to nine. Rustam Pakaya, the chief of Health Crisis Center, gave the latter figure, which was based on information gathered from local hospitals, clinics and regional health offices. He said at least 49 people were injured.

The first quake was felt in at least four countries, with tall buildings swaying in cities up to 1,200 miles away. It was followed by a series of strong aftershocks, further rattling residents.

Telephone lines and electricity were disrupted across a large swath of Indonesia, making it difficult to get information about damage and casualties.

Suhardjono, a senior official with the local meteorological agency who like most Indonesians uses only one name, said a small tsunami, perhaps 3-feet high, struck Padang about 20 minutes after the quake. The Pacific Tsunami Warning Center also reported a small wave.

But most of the damage appeared to come from the ground shaking.

Two people died when a car dealership collapsed in Padang and another was killed by a fire on the fourth floor of a damaged department store, a witness, Alfin, said by phone. Excavation machinery was being used to search the rubble for survivors, he said.

The undersea temblor hit around 6:10 p.m. at a depth of 18 miles, the U.S. Geological Survey said.

In Indonesia's capital, Jakarta, hundreds of miles from the epicenter, office workers streamed down stairwells as tall office buildings swayed. High-rises also were affected in Malaysia, Singapore and Thailand.

Sensitive to the 2004 tsunami disaster, governments issued alerts as far away as Kenya and Tanzania in East Africa, telling people to leave beaches. People in Mombasa, Kenya, crowded into buses after hearing the warning over the radio.

Thailand's National Disaster Warning Center sent cell phone text messages alerting hundreds of officials in six southern provinces, and after the danger past broadcast a statement on television to reassure the public.

In India, officials said the tremor was not felt in the remote Andaman and Nicobar islands, some of which are just 150 miles north of the quake's epicenter. But an alert was issued and authorities were told to take precautions, said Dharam Pal, the regional relief commissioner.

Sri Lankans were told to move at least 660 feet inland.

In Australia, the tsunami warning was lifted after only small rises in the sea level were measured at Cocos Island and the Christmas Islands.

Indonesia, the world's largest archipelago, is prone to seismic upheaval due to its location on the "Ring of Fire," an arc of volcanos and fault lines encircling the Pacific Basin.