Padang, Indonesia  - International rescuers began working Saturday to save thousands of people still buried under collapsed buildings three days after a powerful earthquake devastated Indonesia's West Sumatra province.

The official death toll from Wednesday's magnitude-7.6 earthquake stood at 497, while 301 people were listed as missing and more than 2,800 were injured, according to data from the disaster relief coordination post at the governor's office.

John Holmes of the United Nations humanitarian relief effort estimated Friday that 1,100 people had died in West Sumatra, adding that the death toll was expected to rise.

Rescue teams from Japan, Australia, Switzerland, South Korea and Singapore, wearing brightly coloured uniforms, gathered in the official residence of the West Sumatra governor to coordinate relief efforts with their Indonesian counterparts.

"We are going to search more places where people are still trapped," said Priyadi Kardono, a spokesman for the National Agency for Disaster Management.

"Foreign rescue teams have equipment needed to evacuate victims," he said.

In the ruins of a learning centre where dozens of children, who went there for extra lessons in math and sciences, were buried, Gusti Anola weeped as she watched residents tried to salvage whatever what was left of the buildings.

He only son, 12-year-old Angga Aldio, died in the building and his body was found on Thursday.

"I'm here to pray for son's soul," Anola said, wiping tears from her reddened eyes with her blue headscarf.

"He was my only only son and for him to have died like this devastates me," she said.

The rescue effort had stopped there as workers diverted attention somewhere else, police officer Bendot Dwi said.

Meanwhile, humanitarian groups raced to deliver aid and prevent outbreaks of diseases.

"Up to 80 per cent of homes and other buildings are damaged or flattened, and more than 600 people may still be trapped beneath them," said Rustam Pakaya from the Health Ministry's crisis centre.

Emergency aid now focused on Padang Pariaman district near the provincial capital Padang.

Padang Pariaman mayor, Mukhlis Rahman admitted that not a single emergency tents has been erected in the devastated areas, while survivors have receive no aid assistance.

The fate of hundreds of residents in Padang Pariaman's hinterland, such as in Padang Alai sub-district, remained unknown after landslides buried their homes following Wednesday's quake.

"We're concentrating our efforts today on distributing emergency assistance, such as tents, blankets and foodstuffs," said Hidayat, a field officer of Padang's Red Cross. "We will airlift the aid via helicopters."

The magnitude-7.6 quake struck West Sumatra on Wednesday afternoon, collapsing thousands of homes in Padang and neighbouring districts. It displaced thousands of people and damaged key infrastructure, including telecommunications, roads, bridges and water-supply systems. It was the largest earthquake to jolt the province in recent years.

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 and 500,000 people homeless in Indonesias Aceh province.

Geologists have said that 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. (dpa)