Even if they manage to find food and shelter, the 1.5 million destitute survivors of Burma's Cyclone Nargis still face a major risk from infected wounds, chronic diarrhoea and malaria or dengue.
In Labutta, one of the worst-hit Irrawaddy delta towns, a third of patients had laceration wounds on their backs from the stinging rain and debris whipped up by winds of 190 km (120 miles) per hour, a Burmese doctor told Reuters.
He said sepsis, a rampant infection of the bloodstream that causes organ failure, was widespread two days after the former Burma's worst natural disaster in recent memory.
"These are injuries we have never seen before," he said in Myaung Mya, 50 kms north of Labutta where 80 per cent of buildings were damaged or destroyed, including the hospital which had its roof ripped away.
Many patients suffered from diarrhoea and dehydration, but there was little saline for intravenous drips. Dirty water, a cause of cholera, was a major problem, he said.
The World Health Organisation (WHO) said access to clean drinking water and outbreaks of communicable diseases such as dengue and malaria were a "big concern" a week after the disaster.
But frustration is mounting over the junta's delays in giving visas to foreign disaster experts and its determination to control the distribution of foreign aid inside the country.
"This is the second disaster," Greg Beck, Southeast Asia programme director for the International Rescue Committee.
"First was the cyclone and the surge of water, the second will come if there is no access to food, water and shelter. They will start dying," he said.
UNICEF, the UN children's agency, estimated 20 per cent of children in the worst
affected areas already have diarrhoea and cases of malaria had been reported.
The agency has distributed 15,000 hygiene kits and plans to send another 20,000, as well as build portable toilets in areas where survivors are gathering.
UNICEF has appealed for nearly US$26 million over next six months to improve water, sanitation and hygiene in a country with decaying infrastructure after 46 years of military rule.
Shunned by the West for its dismal human rights record and detention of democracy icon Aung San Suu Kyi, the former Burma receives far less foreign aid than its regional neighbours.
Coupled with the regime's paltry spending on health care - about three per cent of the national budget compared to 40 per cent for the military - Burma's 53 million people face some of the highest rates of deadly diseases in Asia.
Malaria, the biggest killer of children under 5, claims 3,000 lives each year in a country that spends less on healthcare per capita than North Korea.
The junta, which says it will accept "relief in cash and kind", has asked for anti-mosquito bed nets, purification tablets to prevent water-borne diseases such as cholera and other emergency supplies.
But the generals are resisting an influx of foreign workers and equipment such as helicopters and boats to get the aid down to the disaster areas quickly.
"If there is not enough food and shelter soon, people will not survive," Phyusin Ngwethaw of the European Commission's humanitarian office told Reuters.