Aid has begun to arrive in Indonesia's devastated Aceh province in significant quantities, speeded up by the arrival of US military helicopters.
US navy helicopters have begun delivering aid to refugees
But distribution is being hampered by the devastation to local infrastructure wreaked by Sunday's quake and tsunami.
Heavy rain in Aceh is also increasing the risk of cholera and other waterborne diseases.
The Indonesian government says up to 100,000 may have died, but the final total may never be known.
Hundreds of survivors in Aceh swarmed to the provincial airport on Saturday, drawn by the arrival of Seahawk helicopters from US aircraft carrier, Abraham Lincoln, which is moored off shore, as well as other foreign military aircraft.
The vehicles are reported to be carrying food, water and generators. Back on board the Abraham Lincoln, the Americans say they have the facilities to purify up to 90,000 gallons of water a day.
The Americans are also bringing in 80 trucks from the town of Medan across the provincial border.
"We just got here, we're here to help and we're going to keep working until the mission is done... Where they say they need (aid) we will move it," Captain Larry Burt, commander of US Carrier Air Wing Two, told Reuters news agency.
One place which needs immediate attention is the town of Meulaboh on Aceh's south-west coast, which only began receiving aid on Friday. The crew of an Indonesian naval ship which has already arrived said only 200 people were there to meet them, even though the town's population before the disaster was between 40-90,000.
But although relief is now streaming in, the BBC's Rachel Harvey in Aceh says the problem is that there is a shortage of manpower on the ground to help unload supplies, and a shortage of safe places in which to store them.
The chief of the US office for the co-ordination of humanitarian affairs in Indonesia, Michael Elmquist, told the French news agency AFP that it would take weeks to deliver supplies to the isolated areas of Aceh.
"It's a concern and we are desperately doing what we can to find ways of establishing distribution systems in Banda Aceh...
"Helicopters are being used to reach some isolated areas, which will provide some relief. But unfortunately helicopters can bring in only a limited amount of supplies," he said.
Even distributing aid to more accessible areas of Aceh is a monumental task, as a result of the destruction suffered by roads, bridges and telecommunication networks, in addition to the damage to government offices, clinics and military bases.
Some parts of the provincial capital Banda Aceh have yet to be cleared - correspondents say bodies can be seen floating in the city's main river - and other parts of the province have not yet been reached at all.
Increasing the misery for Aceh's survivors was the heavy rain which fell on the province on Saturday.
ACEH: KEY FACTS
Province on the north-western tip of Sumatra
Higher percentage of Muslims than other parts of Indonesia
Gam rebels have fought decades-long separatist campaign
Year-long military crackdown beginning in May 2003 weakened Gam, but failed to capture senior members
In addition to making conditions more uncomfortable for the province's 500,000 or so refugees, it increases the risk of disease.
Another problem complicating relief work is that the province remains under military control, with soldiers engaged in a long-running conflict with separatist rebels.
Both sides said earlier this week that they were suspending hostilities, but there were reports on Friday of renewed skirmishes.
Indonesian President Susilo Bambang Yudhoyono said in a New Year's Eve speech that his country had not suffered such a devastating natural disaster for more than a century.
"Not since the eruption of Krakatoa in 1883 have we been hit so hard by the devastating wrath of nature," he said.
"We mourn, we cry, and our hearts weep, witnessing thousands of those killed left rigid in the streets. We witness those who survive almost losing hope and deep in sadness and confusion."
The Indonesian minister for people's welfare, Alwi Shihab, who has been put in charge of the relief effort, admitted that the government did not know how to handle the tragedy when it first happened.
"At first we had no idea how bad this disaster was," he told the BBC, "then we panicked."
Our correspondent says the government must now make up for lost time and start co-ordinating what is likely to become a massive operation.
There was, however, a piece of good news for the area on Saturday when a man who had been buried under his house in Banda Aceh was discovered still alive.