|Tents and tarpaulin have been delivered to provide temporary shelter to survivors [AFP]
At least 408 people have been confirmed dead after a tsunami triggered by a powerful earthquake hit Indonesia's western Mentawai Islands earlier this week, but officials say the death toll could be much higher.
Harmensyah, the head of the West Sumatra provincial disaster management centre, said on Friday that rescue teams "believe many, many of the bodies were swept to sea".
Bodies have also been found buried on beaches and even stuck in trees across the islands.
More than 400 people are believed to be still missing after three-metre high waves battered the small group of islands, about 280km to the northwest of Sumatra, on Monday.
"Of those missing people, we think two-thirds of them are probably dead, either swept out to sea or buried in the sand," Ade Edward, a local disaster management official, said on Thursday.
"When we flew over the area ... we saw many bodies. Heads and legs were sticking out of the sand, some of them were in the trees. If we add another 200 to the toll it would be at least 543 dead."
Rescue efforts hampered
Bad weather that continues to hang over the western coast has made it hard for relief workers to ferry aid such as tents, medicine, food and water to the islands by boat from the nearest port of Padang, which is more than half a day away even in the best conditions.
Al Jazeera's Wayne Hay, one of the few television journalists on the islands, visited the village of Mantai Barubaru, where 74 houses, two schools and a church were swept away.
|Almost 13,000 people are living in makeshift camps
after their homes were swept away [AFP]
The government, he said, had already begun to deliver disaster relief supplies to the village, a corner of which has now been turned into a collective grave for victims, but strong winds and heavy rain are lashing the area.
Our correspondent reported on Friday that the weather is hampering efforts by small boats to deliver supplies to outlying areas.
The village residents who are driving the boats told Hay the rain makes it hard to see the debris that now pepper the shallow water, thanks to the tsunami surge.
Almost 13,000 people are living in makeshift camps on the islands after their homes were swept away.
Indonesia has dispatched troops and at least five warships to the region, but there is believed to be a need for more helicopters to reach the most isolated communities, some of which lack roads and wireless communications.
Broken alarm system
As the magnitude of the disaster became clear, many began asking whether an expensive warning system - established after the massive 2004 Asian tsunami, which killed at least 168,000 people in Indonesia alone - had failed.
Tsunami survivors have said they had almost no warning that the wall of water was bearing down on them, despite a sophisticated network of alarm buoys off the Sumatran coast.
While an official tsunami warning was apparently issued just after the 7.7-magnitude quake, it either came too late or did not reach the communities in most danger.
"There are suggestions that, in fact, the [early warning system] has never worked properly since 2004," our correspondent said.
One survivor, Borinte, a 32-year-old farmer, said the wave slammed into his community on North Pagai island only 10 minutes after residents had felt the quake.
"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 the AFP news agency on Wednesday.
He said he managed to stay alive by clasping to a piece of wood. His wife and three children were killed.
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, triggered by a 9.3-magnitude quake along the same fault line that caused the 2004 Asian tsunami.
Source: Al Jazeera and agencies