At least 75 people were killed and thousands more trapped underneath rubble after a major earthquake hit Indonesia's Sumatra island on Wednesday, officials said, with fears the death toll would yet rise.

Large buildings including hospitals and hotels caved in, homes fell down and fires raged in the coastal city of Padang, home to nearly a million people, as communications and power remained cut hours after the 7.6-magnitude quake.

"Houses and buildings have collapsed, causing thousands of people to be trapped inside in the rubble," Health Ministry crisis centre head Rustam Pakaya told AFP, adding that a major city hospital was among the destroyed buildings.

Rescue teams and doctors had been sent overland and were expected to arrive in the city in about 10 hours, Pakaya said.

Confirming the death toll, Vice President Jusuf Kalla said there were grave concerns for thousands trapped under buckled buildings.

"The initial level is 75 but it's certain to be higher than that," Kalla told reporters.

Local media reported that panicked residents rushed from their homes during the quake, which struck off Sumatra's west coast at 5.16 pm (1016 GMT), 47 kilometres northwest of Padang.

"A number of hotels in Padang have been destroyed," Indonesian tsunami warning head Rahmat Triyono said, adding the agency did not release a tsunami alert.

The Pacific Tsunami Warning Center in Hawaii however issued a tsunami watch for Indonesia, Malaysia, India and Thailand, but later cancelled it.

"Up to now we haven't been able to reach Padang, communications have been cut," Triyono said.

The quake was felt in the capital Jakarta, 940 kilometres away, and sent frightened office workers streaming out of buildings in nearby Singapore and the Malaysian capital Kuala Lumpur.

"The shaking was the worst I had ever felt," Yuliarni, a resident of Pariaman district outside Padang, told TVOne news channel.

"Houses have collapsed, the lights and electricity were cut off... People were fleeing to higher ground and some were hurt," she said.

Quake caused landslide

The quake caused a landslide that destroyed houses at Lake Maninjau inland from Padang, local resident Hafiz told the channel, and the airport was also closed for damage.

"Part of the roof of the arrival hall at the Padang airport collapsed but nobody was injured. The runway is okay. The airport has been closed but will reopen at 7am tomorrow," Hariyanto, an official of airport operator company Angkasa Pura II, told AFP.

Geologists said Padang, which lies near the colliding Indo-Australian and Eurasian tectonic plates, was vulnerable to more quakes and tsunamis.

"There will be aftershocks but it's difficult to predict whether there will be a bigger quake," Geological Disaster Mitigation and Volcanology Centre head Surono told AFP.

"There are three big volcanoes in West Sumatra — Merapi, Talang and Tandikat. We fear that this quake might cause volcanic eruptions there," he said.

Experts have said the city is most at risk from a final segment along the zone shifting to unleash a massive amount of energy.

The zone's other segments have already cracked, including a large portion off Aceh, at the northern tip of Sumatra, which triggered the 2004 Indian Ocean tsunami which killed more than 220 000 people.

Plans for evacuation shelters and improved roads to provide better escape routes from tsunamis since 2004 have mostly not been realised.

World Vision's Indonesian emergency head Jimmy Nadapdap said in a statement the charity would attempt to send out a disaster survey team to the affected area on Thursday morning.

"It is critical that we get people into the quake zone as soon as possible to find out what has happened," he said.

"If buildings have collapsed then people are likely to be in urgent need of food, water and especially shelter. The injured will also need medical assistance."

Indonesia sits on the Pacific "Ring of Fire," where the meeting of continental plates causes high volcanic and seismic activity.

A quake on the main island of Java earlier this month killed 123 people.

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AFP

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