A social ministry official said on Thursday the death toll had now risen to 6,234.

"More than 22,000 patients have been treated in 29 local hospitals, field hospitals, health centres and mobile clinics," the UN Office for the Coordination of Humanitarian Affairs (OCHA) said in a statement.

"However, local health facilities continue to be overwhelmed, especially as the population has no homes to which to return."

Officials say even people who are healthy and in no need of further medical treatment try to stay in hospitals because of lack of shelter, food and clean water in their home areas.

Health Minister Siti Fadillah Supari said on Wednesday the government was evacuating patients from hospitals in the immediate quake area to more distant cities to relieve overcrowding.

The quake, which struck around dawn on Saturday, levelled entire villages with homes reduced to piles of wood, tiles and tin.

There were no signs of disease outbreaks so far, but medicines were being sent to affected areas to prevent any epidemic. Survivors were being immunised against measles.

The quake affected hundreds of square kilometres in an area that is densely populated but where roads and communications are often poor, adding to the difficulties of reaching the more remote areas. The disaster also damaged roads and bridges.

Aid from the Indonesian and foreign governments, the UN, and private agencies has been flowing into the region in increasing amounts, although many survivors still complained they lacked critical help.

However, officials say that in general the aid effort is going well and some hiccups in a major disaster are unavoidable.

"I think the Indonesia system works. It has been working very well," said Jan Egeland, the UN undersecretary-general for humanitarian affairs, speaking by phone from Paris.