The toll from a tsunami which smashed into Indonesia rose sharply past 270 on Wednesday as rescuers reached the remote islands hit hardest by the disaster and found scenes of devastation.

At least 10 villages were flattened when the tsunami triggered by a 7.7-magnitude offshore earthquake pounded the Mentawai islands late Monday off the west coast of Sumatra.

"We've recovered 272 bodies. At least 412 people are still missing," West Sumatra provincial disaster management official Ade Edward told AFP.

Survivors said they had no warning that the three-metre (10-foot) wave was bearing down on the Mentawais, a popular destination for foreign surfers but otherwise a poor and neglected outpost in the vast Indonesian archipelago.

Borinte, 32, a farmer from Detumonga village on the coast of North Pagai island, said he managed to stay alive by clasping to a piece of wood. His wife and three children were killed.

"About 10 minutes after the quake we heard a loud, thunderous sound. We went outside and saw the wave coming. We tried to run away to higher ground but the wave was much quicker than us," he told AFP.

The first images from the scene of the disaster, broadcast late Wednesday on Indonesian television, showed shell-shocked villagers picking through the sodden ruins of their homes.

Several hundred kilometres away on the central island of Java, another 29 people were killed when the country's most active volcano, Mount Merapi, erupted on Tuesday, spewing searing clouds of gas and lava into the sky.

Officials said almost 42,000 people had fled to temporary shelters around the nearby city of Yogyakarta, but there were fears for the fate of thousands more who had refused to budge.

The United States and several of Indonesia's neighbours pledged help for a nation which often finds itself battling calamity, although Jakarta said it did not see a need for foreign assistance.

Several Australian tourists were caught in the tsunami, getting more than they bargained for on a surfing holiday.

One group survived after their boat was picked up by the wave and slammed into another, creating an explosion. Another group of nine surfers was found alive after being reported missing.

Dave Jenkins, the founder of SurfAid International, a non-profit community health organisation which operates on the islands, earlier told AFP the official toll would rise beyond the 154 reported on Wednesday morning.

"We have staff in a lot of villages and we have boats out there. There's been a lot more destruction and fatalities and people missing than has been reported," he said.

"These islands are extremely remote. There are no roads and there are no phones in a lot of places," he added.

The tsunami surged as far as 600 metres inland on South Pagai island, officials said. On North Pagai, a resort and almost 200 houses were flattened.

"When the tsunami struck there were dozens of fishermen out at sea. Their bodies were found the next morning floating on the water or cast ashore on the beach," provincial disaster management chief Harmensyah said.

Medical personnel flew in on helicopters but rescue efforts have been hampered by bad weather and poor communications to the islands, which are about half a day's ferry ride away from the port of Padang on Sumatra.

Troops and naval personnel were also dispatched to the area. Indonesian western fleet commander Marsetio said at least five warships were on their way.

President Susilo Bambang Yudhoyono cut short a visit to Vietnam for a summit of Southeast Asian leaders and was on his way to the Mentawais, which he should reach on Thursday, officials said.

US President Barack Obama, who lived in Indonesia as a boy and is due to return there on an Asian tour next month, voiced his sadness over the deaths and pledged US help.

"As a friend of Indonesia, the United States stands ready to help in any way," he said.

White House spokesman Robert Gibbs said that he was not aware of the disaster having any effect on Obama's planned trip to Indonesia.

Indonesia straddles a region where the meeting of continental plates causes high seismic activity. It has the world's largest number of active volcanoes and is shaken by thousands of earthquakes every year.

A 7.6-magnitude earthquake last year in Padang killed about 1,100 people, while the 2004 Asian tsunami -- triggered by a 9.3-magnitude quake along the same faultline -- killed at least 168,000 people in Indonesia alone.