Aid workers say they are still struggling to reach or even locate displaced people in the devastated Indonesian province of Aceh.
No-one is sure how many people are on the move
Roads have entirely disappeared in some places along the badly-hit west coast and helicopters visiting villagers there can carry only limited supplies.
UN aid co-ordinator Michael Elmquist said there were also reports of refugees having fled into the hills.
Aceh was further traumatised on Thursday by a powerful aftershock.
Mr Elmquist told the French news agency AFP that he thought the aid operation in Aceh, the region worst hit by the 26 December Indian Ocean tsunami, was about to reach "its peak in intensity", but that distributing assistance remained a problem.
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
"We still need to get much more assistance out to the west coast but it's very cumbersome and challenging to do that," he said.
However, a BBC correspondent in Aceh, Jonathan Head, says there is nevertheless a lot more assistance available to the province than just two or three days ago.
Finding other routes
The UN is considering transporting aid on the long land route from Medan to the devastated town on Meulaboh, through the highlands, because it would be more cost-efficient than using helicopters.
US helicopters are flying dozens of missions a day to drop supplies to those communities yet to be reached by aid workers on the west coast.
One such town is Teunom, which the BBC's Andrew Harding visited on Wednesday.
Our correspondent said that with only one bag of rice left between 1,600 survivors, some had been reduced to hunting for buried tins of food in the rubble.
Aid workers are also aiming to gather information on where exactly the refugees are. Many have made their own make-shift camps, although the Indonesian government has reportedly agreed to establish proper camps along international health guidelines.
About 500,000 survivors have been left homeless in Indonesia, and without proper care, they too are at risk. Dangerous infections are sneaking into superficial wounds, said Dr Ronald Waldman of the World Health Organisation.
Refugees are also suffering serious psychological trauma, and frayed nerves were tested further after dawn on Thursday when a 6.2 magnitude aftershock shook the provincial capital of Banda Aceh.
Many are extremely traumatised by their ordeal
Many people panicked and ran out of their homes, but there were no reports of casualties.
The death toll in Indonesia is currently more than 94,000, and is expected to rise further.
About 1,000 of the dead are teachers, the Indonesian government said on Wednesday, adding that replacements would be sent to Aceh as soon as possible in order to allow some schools to begin operating in the province again by 20 January.
Another impediment to aid distribution is isolated skirmishing between the Indonesian military and separatist rebels in Aceh.
On Thursday there were unconfirmed reports of gunshots exchanged between the two sides near the airport in Banda Aceh, and rebels firing from a fishing boat in Lhoknga, about 40km (25 miles) south-west of the city.