But in the absence of an effective distribution system, agencies are having to use the services of local residents and organisations to channel the aid to the needy.
Field hospitals may be more accessible than government clinics
They are also having to contend with the local bureaucracy, which they say is slowing down their ability to deliver aid to victims.
"We have just been told of a directive from the president's office that all aid must be routed through the government," says Dr Ulrich Stiassny of the Austrian Samaritans.
"They are happy for us to bring the aid into the country, but they want it delivered through their channels."
What many of the aid workers voice privately is that the government's aid distribution network does not touch all parts of the country.
And while many of the facilities set up by the government are well organised and stocked with supplies, they are only available to those victims who manage to reach the camps.
"The main hospital in Galle, for instance, is very well equipped. It has enough doctors, nurses and plenty of medical supplies," Dr Stiassny says.
"But not everyone can get to it. There is no public transport. So how can it benefit those victims who are stuck in far-flung areas?"
Update: India is delivering to some remote islands.
The Indian army says planes have dropped food and water to tsunami survivors on all the inhabited islands in the Andaman and Nicobar chain.
There was criticism that aid has been slow to reach survivors, thousands of whom may be sheltering on high ground.
The military commander in charge of the relief effort said the most remote locations had now been reached.