Although less pressing than the need to ensure access to clean water, food and shelter, treatment of post-traumatic stress disorder (PTSD) could not be ignored if tsunami-shattered communities were to rebuild, they said.

"Recovery cannot take place unless we remain aware of the emotional effects and the mental health consequences," Jonathan Davidson of the Department of Psychiatry at Duke University in the United States told a news conference.

"The task is likely to be a long one and many survivors may experience persisting psychological problems, but we must believe that recovery can be achieved," he told a mental health conference in Bangkok.

Davidson said his estimate of a 50-90 percent rate of mental trauma was based on studies from previous major natural disasters.

In Thailand, where more than 5,400 people were killed in the Dec. 26 disaster, around half of them foreign tourists, some 10,000 people have already been treated by roving teams of mental health workers, the Health Ministry says.

Somchai Chakrabhand, head of its Mental Health Department, said around 30 percent of people in tsunami-hit areas were displaying signs of moderate PTSD, such as an inability to sleep or look at the sea.

A further 20 percent were "very significantly affected", he said.

The conference is looking at different ways of treating psychological trauma to come up with treatment regimes suitable for the diverse cultures of tsunami-hit India, Sri Lanka, Indonesia and Thailand.

In Indonesia’s Aceh, the devoutly Muslim province which bore the brunt of the killer waves, many people have already turned to the mosque to help cope with the mental fallout.

It was vital that help did come, whether from drugs or counselling by doctors, nurses, friends, family or religious leaders, Davidson said.

"These individuals will definitely need help. The question is what kind of help," he said.