The World Health Organization has warned that disease in the aftermath of southern Asia's tsunami disaster could kill as many people as the deadly waves and earthquake have.

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 around 55,000 and is expected to rise.

But with relief officials warning of possible cholera epidemics and malaria, David Nabarro, head of crisis operations for WHO, said the main threat to life now is communicable diseases associated with a lack of clean water and sanitation.

Nabarro said local hospitals and health services are already overwhelmed by the initial impact of the earthquake, and so are less able to cope with people who may fall ill.