Padang, Indonesia  - At least 529 people were killed and 2,150 injured in a powerful quake that struck Indonesia's West Sumatra province, officials said Thursday as rescuers struggled to save thousands still trapped under rubble.

In the provincial capital, Padang, which was the hardest-hit area in Wednesday's magnitude-7.6 earthquake, as many as 376 people were killed, said Novianto, an official at the Social Affairs Ministry's coordinating post.

Novianto, who like many Indonesians goes by one name, said the death toll was likely to rise.

Thousands of people were still trapped under rubble, the National Disaster Management Agency said on its website.

Earlier, Health Minister Siti Fadilah Supari said thousands of people might have been killed in the quake, while damage could be worse than that done by a 2006 earthquake in the central Java city of Yogyakarta where more than 5,800 people were killed and more than 150,000 buildings destroyed or damaged.

The deaths occurred in five districts of West Sumatra, said Tugio Basri, an official at the Social Affairs Ministry's coordination post in Jakarta.

Wednesday's quake also displaced thousands of people and damaged key infrastructure, including telecommunications, roads, bridges and water supply systems, witnesses said.

Another quake, measuring 7 on the Richter scale, jolted adjacent Jambi province about 225 kilometres south-east of Padang Thursday morning, destroying or damaging hundreds of buildings and making thousands homeless.

There were no reports of injuries or deaths from the second quake, officials said.

"There was panic, but yesterday's quake was felt stronger here," Romi Suwanto, an official in Jambi's Kerinci district near the epicentre of the quake, said Thursday.

Television footage from Padang showed scenes of devastation with hundreds of buildings - including a four-story religious court, shops and homes - flattened. One shot showed a buried victim's foot sticking out from the rubble.

TV One showed rescuers using a mechanical excavator to remove debris at a school where locals claimed up to 60 students were trapped. Seven people were rescued from the building and four found dead, the channel said.

"I will be waiting until they find my daughter," a weeping mother whose 13-year-old was believed trapped under the rubble told TV One.

Rescue workers made up of soldiers and police officers were shown pulling several female bodies from the ruins of a three-story school building as relatives of the missing watched.

The Dr M Djamil hospital, the largest public hospital in the provincial capital, was overwhelmed with the injured and the dead. The hospital itself suffered major damage, with upper floors collapsing, forcing doctors to treat patients outside in makeshift tents, the floors of which were covered with in bloody swabs, discarded syringes and mud from the intermittent rain.

Dadang Hanidal, head of the regional disaster coordinating agency, was quoted by the Kompas daily as saying that up to 200 guests remained trapped under the rubble of the collapsed Hotel Ambacang in Padang.

Survivors spent another night outdoors in the dark with electrical power cut off as officials in the province expressed hope of restoring power within the next two days. Rescue efforts have been hampered by the disruption of telecommunication lines while roads into the city were also blocked by landslides.

President Susilo Bambang Yudhoyono flew to Padang immediately after arriving Thursday in Jakarta from the Group of 20 summit in the US city of Pittsburgh.

"My job is to make sure that the system works," Yudhoyono told rescue officials in Padang.

"Don't underestimate this disaster," he said. "It is better to overestimate than underestimate it."

Six government ministers flew Thursday to Padang, and two Hercules C-130 military cargo aircraft departed from Jakarta carrying doctors and relief supplies such as tents, medicines and food.

Wednesday's quake struck at 5:16 pm (1016 GMT) off the western coast of Sumatra. A magnitude-6.2 aftershock followed 22 minutes later.

The districts of Padang Pariaman and Sungai Giringging are among the hardest-hit areas with hundreds of homes collapsed, officials said.

The government approved 250 billion rupiah (about 26 million dollars) in cash aid for victims, officials said, explaining that the cost of repairs of infrastructure and transport facilities damaged by the quake is still being calculated.

Indonesia, the world's largest archipelago nation, sits on the Pacific "Ring of Fire," the edge of a tectonic plate prone to seismic upheaval.

A major earthquake and subsequent tsunami struck in December 2004, leaving more than 170,000 people dead or missing in Indonesia's Aceh province and 500,000 people homeless.

Wednesday's quake occurred along the same fault line.

Geologists have said Padang, a low-lying city of 900,000 people, risks being swallowed by a tsunami in the event of an earthquake similar in magnitude to the one that triggered the giant 2004 wave.

An earthquake last struck Padang in 2007, killing dozens of people and injuring scores of others. dpa