Although relief organizations are distributing medical supplies to prevent the outbreak of disease, the main focus is still on dealing with the wounded, said Jamie McGoldrick, an emergency relief coordinator of the U.N. Office for the Coordination of Humanitarian Affairs (search) in Geneva.
"Diseases will start to come through in the next few days," McGoldrick told The Associated Press. "No doubt people will be affected, kids are drinking stagnant water."
Governments in 11 nations are still trying to determine how many were killed in the devastation wreaked by Sunday's quake and the tsunamis it caused. The death toll now stands at more than 60,000 and is expected to rise.
It is still impossible to visit some isolated islands off the northern coast of Sumatra and assessments can only be made from the air, McGoldrick said.
"Populations we haven't reached yet may suffer from disease," he said.
With relief officials warning of possible cholera epidemics and malaria, Dr. David Nabarro, head of crisis operations for the World Health Organization, has said that "there is certainly a chance that we could have as many dying from communicable diseases as from the tsunami."
Nabarro said the main threat to life now is communicable diseases associated with a lack of clean water and sanitation.
"The initial terror associated with the tsunamis and the earthquake itself may be dwarfed by the longer term suffering of the affected communities," he warned.
Hospitals and health services already are overwhelmed and may not be able to cope with people who fall ill with disease, Nabarro said.
Worst-hit have been Indonesia, Sri Lanka, India, Thailand and the Maldives. But Malaysia, Myanmar, Bangladesh, Somalia, Tanzania, Seychelles and Kenya have also reported deaths from the tidal wave that sped across the Indian ocean Sunday morning.
The United Nations has sent disaster assessment teams to the affected countries and relief organizations are distributing supplies. The global body is also starting to put together an appeal for international aid.
Essential supplies are already arriving in the region, but "need to be properly coordinated so that those who most need help get it in these vital early hours and days after the disaster," Nabarro said.