Conditions are deteriorating on the quake-hit Indonesian island of Nias, according to local health officials.
A lot of aid has arrived on Nias but distributing it is difficult
One local worker told the BBC that diarrhoea, already a problem before the quake, had become an epidemic, exacerbated by a lack of clean water.
She said that cases of malaria had also risen.
Relief efforts are being hampered by poor weather and damaged infrastructure on the island, as rescue workers struggle to reach outlying villages.
The UN has confirmed that more than 500 people were killed in Monday's earthquake off Indonesia, and at least 1,000 are feared dead in total.
Local health worker Rhamani Oktavianu said that the people of Nias were already suffering from diarrhoea before the quake, but that the problem had now got worse because hospitals had been destroyed and some parts of the island were cut off from medical supplies.
Gunung Sitoli remains without electricity, and the water purification system is down.
Aid is reported to have become bottle-necked at mainland ports and airports, and broken bridges and roads are making travel away from Gunung Sitoli impossible for anything but motorbikes.
"We haven't seen any aid come this way yet. Helicopters have landed but only to take the injured away," said Lelly Arnita Ndruru, 20, a shopkeeper in Sisarhili village 50 km (31 miles) south of Gunung Sitoli.
High seas have forced two boats loaded with aid back from the neighbouring island of Simeulue.
The UN remains hopeful that a landing craft stocked with food and other essentials will soon arrive in Nias from neighbouring Aceh.
The Australian military also expects a floating hospital to arrive off Nias early on Saturday.
Earlier on Friday, rescue workers were reported to have abandoned the search for survivors in Gunung Sitoli.
But a local police chief later told the BBC that rescue efforts were continuing.
On the neighbouring Banyak islands, the extent of the damage is still not clear.
Earlier in the week, an Indonesian disaster official said an estimated 200-300 people had died on the island chain, but on Friday a village chief said the islanders had suffered no casualties, although they were desperate for food and water.
Simeulue casualties are reported to be low, because the flimsy buildings lacked impact when they collapsed.
But the devastation is said to be high. "In some villages, there is something like 100% destruction," said UN spokeswoman Imogen Wall.
On Friday, an interim tsunami early warning system for the Indian Ocean was due to go live.
But so far only six nations have taken the necessary measures to receive the warnings.
They will receive data from detection centres already established in the US and Japan.
Nations across the Indian Ocean agreed three weeks ago at a UN meeting that, while waiting for a full-scale tsunami warning system to be designed and built, they should make use of systems already available - the Japanese Meteorological Agency and the Pacific Tsunami Warning Centre in Hawaii.
From Friday, seismic data collected by these two centres will be sent to the six nations which have already set up units designed to collect and disburse this information.
The UN agency co-ordinating the system - the International Strategy for Disaster Reduction - believes other nations will have such units soon.
The Japanese Meteorological Agency is aiming to send fax messages warning of a possible tsunami within 30 minutes of detecting tell-tale earth tremors.