Countries hit by the worst earthquake and tsunamis Sunday struggled to find and bury their dead and get water and other emergency supplies to survivors Tuesday.
They also face greatest danger in coming days as there could be epidemics of intestinal and lung infections unless health systems get the help they badly need.
"The biggest threat is from the spread of infection through contamination of drinking water and putrefying bodies left by receding waters," world health experts in Geneva said.
Homeless people fearing another wave shelter in public buildings, schools and on high ground. There is a shortage of clean water and provisions.
The death toll in the whole area has reached more than 25,000 people and the figure is still gradually coming up.
Responding to these countries in bad need of relief aid, the United Nations said hundreds of relief planes packed with emergency goods would arrive from about two dozen countries within the next 48 hours.
The real scale of the disaster in the region is still unclear as chaotic government officials in the countries warn many thousands listing as missing may have been dead.
Sri Lanka appears to have been the worst hit for the moment with more than 12,520 dead, along with India which reported 7,000 killed. Nearly 1,000 people were killed in Thailand.
In Galle, a city 100 km south of Sri Lanka's capital, rows of bodies covered in plastic sheets or mats were laid out in the hospital as more than 700 dead have already been taken away by tractors for mass burials.
Local residents are still looking around the hospital ground to identify the body of their loved ones. Most of them have to cover their nose and mouth with cloth or tissue papers to block off the odor of the decomposing bodies.
Sad voices of college student volunteers could be heard through loudspeakers in the city, calling continuously and desperately for the missing people who might have been already swept away by the tidal waves to "contact their families."
"We offer help to dead people's family, we give them food and clothes. I wish this not happen again," said Asanka Maddnma Arachch, a student volunteer who announced the missing list by turns with other volunteers.
In Indonesia where nearly 5,000 have reported killed and the figure is very likely to go up as aid workers and government officials gradually arrive in the worst hit area since late Monday. Indonesian Vice President Jusuf Kalla said the toll there could be much higher and up to 100,000 people may have been injured.
In New Delhi, Prime Minister Manmohan Singh announced a relief of Rs one lakh to the next of the kin of each of those killed from the Prime Minister's National Relief Fund.
He would also undertake an aerial survey of the affected areas Tuesday. The death toll climbed to nearly 7,000 in India as the scale of death and destruction began unfolding over 36 hours after the disaster struck.
Weather officials in the region warn of more high waves over the next day or two and urge people to stay away from the shore. " The tsunami will only die down slowly like a ripple, and people have to expect more waves before they gradually subside," said experts from the Meteorological Department of Tamil Nadu state, one of the worst-hit areas.
People in Sri Lank's Galle are looking hopelessly at their ruined buildings or damaged households as a way to keep an eye on whatever is left since most of them are very poor fishermen, but none dare to move a bit closer to the shore, as threatening tides still surge high after Sunday's killing tsunamis.