The earthquake-hit Indonesian island of Nias is facing a critical situation because of shortages of water, shelter and medicine, aid agencies say.
Damage to the infrastructure is hampering the aid effort
Supplies have been arriving slowly, but the main town of Gunung Sitoli remains without running water and power.
The search for survivors and bodies is continuing on the devastated island, which has been rattled by aftershocks.
The United Nations says more than 500 people were killed in Monday's quake, but up to 1,000 are feared dead.
At least 11 foreign tourists who had been missing for three days were found alive on Thursday in Nias, the Swedish foreign ministry announced.
A search helicopter found the foreigners - two Swedes, two French people, one US national, one German, three Britons and two Canadians - in a surfing resort.
"We're working on how to get them back," said Sweden's ambassador in Jakarta, Lennart Linner.
On Wednesday a young boy was pulled out of the rubble and rescue workers are hopeful of finding more people alive.
Hundreds of people - including foreigners - remain missing.
Indonesian President Susilo Bambang Yudhoyono arrived for a tour of the island on Thursday, and is currently visiting the most damaged areas.
The tremor caused panic across the Indian Ocean region, which is still reeling from the huge tsunami that killed some 300,000 people in December - two-thirds of them in Indonesia.
Monday's 8.7-magnitude quake was less than 200km away from the epicentre of the quake that triggered the earlier disaster.
Damage to the tiny airport on Nias means that only light aircraft and helicopters are able to land, slowing the delivery of aid.
More is being sent by sea, but that will take much longer to get there.
Heavy rain has also slowed the rescue efforts, although there was a slight improvement in the weather on Thursday.
So far, survivors have been left largely to fend for themselves, sifting through the wreckage of multi-storey concrete buildings to find the bodies of their loved ones, BBC correspondents report from Nias.
Hungry residents of one village in the southern part of the island say they have not received any help.
People have been sleeping outside their homes - if they still have them - fearing further tremors.
Aid agencies are aiming to intensify the distribution of water and medical supplies.
Oxfam has flown in tents, food and water, body bags, fuel and basic medical supplies.
More specialist aid equipment including water pumps, water tanks and communications equipment is expected to be flown in on Friday, the charity says.
Australia is sending a third military aircraft after first reports from its rescue officials said the situation was worse than expected.
"It has been a very significant humanitarian crisis," Australian Foreign Minister Alexander Downer said.
Nias Island: Two UN water purification plants are expected on Thursday, as well as more than 300 tonnes of aid. Heavy-lifting equipment had been sent to the area, but there are problems in getting it ashore. The US has despatched a 1,000-bed hospital ship, due in six days.
Simeulue: 200 tonnes of food aid already distributed, mostly by aid workers already on the island because of December's disaster. An estimated 12,000 people need shelter.
Banyak Islands:Unconfirmed reports say several hundred people have died. Parts of the island appear to have sunk by up to a metre (3 feet).