A shattered infrastructure is stopping the delivery of aid in Indonesia's quake-ravaged Aceh province.
Parts of Banda Aceh were obliterated. (Photos: Digitalglobe)
Some 500,000 people are without homes and desperately need help, a government spokesman told the BBC.
The official Indonesian death toll from Sunday's disaster is nearly 80,000, but the Health Ministry said it would probably rise to more than 100,000.
The government said it had given up trying to provide accurate death totals, now the numbers were so large.
In Jakarta, the government announced it would host an international summit next week, to address the regional crisis.
The BBC's Andrew Harding in Aceh's provincial capital, Banda Aceh, says a logistical nightmare awaits the aid operation now taking shape.
He says foreign doctors have arrived in force at the main hospital in the city, but many essential items are in desperately short supply.
Infections are spreading among the injured, while food and clean drinking water - as well as the fuel needed to deliver it - remain scarce. The city's petrol depot was severely damaged in the disaster.
Another problem is that government offices, clinics and military bases have all been destroyed and many of the people who would normally run these institutions are dead.
In Banda Aceh, bodies still lie on the streets. One resident told the BBC: "At first when we saw the dead bodies we took them away. But after the fourth day we didn't do it any more."
A UN official, relief co-ordinator Margareta Wahlstrom, said aid agencies were delivering mobile offices to the disaster zone so that aid workers could be "totally self-contained".
A base camp for international aid workers was expected to be ready by Friday, the UN said.
Large areas of the south-west coast of Sumatra, the island where Aceh lies, as well as a string of smaller islands nearby, remain completely cut off.
A worker with medical charity MSF, who flew over 10-15 towns and villages on the coast on Friday, said "devastation" was not a strong enough word.
"Basically all the villages on the coastal line are completely gone, there is nothing, in some places even the foundations of the houses have disappeared," Sabine Rens told the BBC.
An Indonesian naval ship carrying marines and medical teams has now anchored off devastated coastal town of Meulaboh, which has been badly hit.
The first eyewitness accounts of Meulaboh are also starting to emerge. The ship's crew said that only 200 people were there to meet them, even though the town's population before the disaster was between 40-90,000.
One woman who survived the disaster described how her clothes were ripped off by the force of the waves and said that she survived by clinging to the minaret of a mosque as the water surged around her.
Roads and airstrips in the region have been washed away and its ports destroyed, Indonesian presidential spokesman Andi Mallarangang told the BBC.
He said fuel for the naval vessels being used to access the worst-hit areas was being transported by truck from the town of Medan, a 24-hour drive away.
Some 10 helicopters had been made available, he said, but they could not carry large cargoes or land in water-logged areas.
One further problem complicating relief work in Aceh 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.