Survivors claim that the tsunami warning system failed to alert them to the threat.
The race is on to deliver aid to remote islands devastated by a recent tsunami.
More than 400 people have been killed and hundreds more than been listed as missing.
Almost 13,000 people are living in makeshift camps after their homes were wiped out in the killer wave.
Indonesia battled Friday to deliver aid to remote islands where a tsunami has killed over 400 people, as bodies lay strewn on beaches and buried in debris days after the wave hit.
Disaster response officials believe the final death toll from the huge wave that pummeled the Mentawai island chain off the west coast of Sumatra Monday could exceed 600, with many victims sucked out to sea as the tsunami receded.
Almost 13,000 people are living in makeshift camps on the islands after their homes were wiped out in the killer wave, which was triggered by a powerful 7.7-magnitude earthquake.
Survivors in a village reached by an AFP photographer said as many as 30 of the community's 100 children had been killed. One man complained they still had not received any assistance from the government.
Elsewhere in the disaster-prone archipelago, the nation's most active volcano, Mount Merapi in central Java, was spewing lava and searing gas, after an eruption on Tuesday killed 34 people.
Volcanologist Heru Suparwoko said the clouds were "definitely dangerous" for people who had refused to obey orders to evacuate the danger zone.
Some 50,000 people have fled to temporary shelters but many are returning to their fields on the volcano during the day, despite the threat of another deadly eruption.
On the Mentawais, a legendary destination for foreign surfers but an otherwise poor and neglected part of Indonesia, officials said helicopters had started dropping aid on Friday.
"We've started sending relief supplies, which are still limited but enough for the people to survive," national search and rescue spokesman Gagah Prakoso said.
The latest official death toll from the tsunami stood at 408, with 303 still listed as missing. Officials said as many as 200 of the missing were not expected to be found alive.
Bad weather has hampered efforts 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.
Some aid workers said they had been stuck in Padang for days, waiting for a ride to the Mentawais.
Shortages of aviation fuel as well as a lack of roads and phone communications on the affected islands were also limiting aid distribution, officials said.
Dave Jenkins of independent health agency SurfAid International, which is based in the Mentawais, said: "Bad weather is forecast and a severely challenging situation has been made a lot worse."
"We need to keep people alive, warm and fed, and fight disease outbreaks. After that we can move into the reconstruction phase," he said. "It's challenging and people need to coordinate much better."
Australia announced assistance of the equivalent of $1 million while the European Commission released 1.5 million euros ($2 million) in aid.
"Indonesia is currently addressing a multitude of emergencies, whose cumulative impact is putting local capacity under severe strain," European aid chief Kristalina Georgieva said.
UN Secretary General Ban Ki-moon said the United Nations stood ready to assist. The United States and several Asian countries have also offered help.
President Susilo Bambang Yudhoyono visited the area Thursday and told survivors the government was doing everything it could.
But he also advised people to move from coastal areas prone to tsunamis, saying this was the "only long-term solution".
Officials have batted away questions about why an expensive warning system -- established after the 2004 Asian tsunami killed almost 170,000 people on Sumatra and nearby islands -- failed to alert people on the Mentawais.
Survivors said the only warning they received was the "roar" of the wave as it sped towards them shortly before 10 pm, even though an official tsunami alert had been issued in Jakarta.
An official responsible for the warnings blamed local authorities on the Mentawais for failing to pass on the alert, telling reporters: "We don't feel there was any mistake."