The tsunami that ripped through coastal villages across southern Asia, killing at least 25,000 people, brought the specter of an epidemic, mobilizing international relief organizations in New York yesterday to address what could prove the most costly disaster in history.

A 9.0-magnitude earthquake took place deep beneath the Indian Ocean Sunday, 150 miles off the coast of Indonesia. While it was neither the most powerful earthquake nor the largest giant wave ever recorded, its widespread tidal effect across 10 densely populated countries raised the death toll and displaced millions.

The disaster put pressure on governments in the region to develop more effective warning networks, like one that has been used in the Pacific since 1965, a year after a 9.2-magnitude earthquake produced a tsunami that hit Alaska. That network is administered by the U.S. National Oceanic and Atmospheric Administration’s office at Hawaii.

Officials of governments in the region said the cost of such a network was prohibitive, the Associated Press reported.

Officials in Thailand issued the only warnings Sunday in radio broadcasts, and they vastly underestimated the strength of the tsunami.

Though Indonesian villages were pummeled within minutes, one precious hour separated the moment when the earthquake struck and the time when waves washed over the shores of Thailand. After 2 1/2 hours, the deluge traveled 1,000 miles and swamped Sri Lanka, eventually hitting Malaysia, the Maldives, Myanmar, and Bangladesh as well.

The death count in Sri Lanka rose to 12,000 yesterday, a number so high that in some areas the authorities ran out of room for the bodies, which quickly began to rot in the high humidity and heat.

Across Thailand’s southern beaches, home to vacationers from colder climes, hundreds of dead were reported, with 19 embassies, including the American mission, setting up makeshift consular offices to help replace passports and other valuables lost at sea.

At India, whose southeastern coast in the province of Tamil Nadu was hammered by waves as tall as buildings, 4,000 people have died, according to reports from news services.

Indonesian government officials put their nation’s death toll at close to 5,000, though the number could double when the full extent of the damage becomes known.

Hard-hit provinces remain incommunicado. The Indonesian province of Aceh in northern Sumatra, 150 miles from the epicenter, was hardest hit. At least 3,000 people in the capital of Banda Aceh, a city of 400,000, were reported dead.

“I kept trying to call my family every 15 minutes to reach them, but the communication wasn’t working,” Eddy Lamno, a 29-year-old political refugee who lives in Woodside in Queens, said yesterday. Mr. Lamno is one of about 200 Acehnese in the United States. They are mainly political refugees who have fled the province since a secessionist movement prompted the Indonesian government to declare martial law there. He was unable to get in touch with his family, many of whom live near the beach.

“It’s really horrible for me,” he said. “The worst part hit by the earthquake and tsunami is my town. My mom and my brother live in Banda Aceh and my sister and older brother live in western Aceh – which is the worst part. They are even closer to the epicenter.”

Other communities in the city whose hometowns were hit by the tsunami gathered for prayer vigils and around television sets and computers to await news from loved ones.

Secretary of State Powell said eight Americans died in the tsunami.

Since the last earthquake and tsunami of similar size, 40 years has passed and the earth’s population has doubled. The devastated countries – India, Sri Lanka, Indonesia, Thailand, the Maldives, and countries of the coast of Africa – have led that growth.

Last year’s earthquake that struck Bam, Iran, killed 26,000 people in seconds and caused hundreds of millions of dollars in damages. The devastation of Sunday’s earthquake and resulting tidal wave spanned thousands of miles from Indonesia to as far away as Somalia, where villagers were said to have disappeared.

“Bigger waves have been recorded, but no wave has affected so many people before because we’ve had a population explosion,” Jan Egeland, the United Nations undersecretary-general for humanitarian affairs and emergency relief coordinator, said at a press conference shown on the Web. While it was too early to tabulate the disaster’s cost, he estimated it would be “many billions of dollars.”

As the death toll continued to rise, relief organizations worried about the health threat that decomposing corpses and sullied water supplies posed to survivors, many of whom lost their homes.

“Now you worry about water-borne disease. Disease carried by water is a hauntingly efficient way to carry bacteria,” the emergency director of the International Rescue Committee, Gerald Martone, said. “It’s a weapon of mass destruction when water gets contaminated.” Mr. Martone’s group was one of the few international aid organizations in Aceh before the tsunami struck. He has not heard from the 20-person team working there.

“It’s incredibly anxiety-producing to not know the welfare of your own staff,” he said. Far luckier were the field offices of international relief organizations in other affected countries. They have been among the first on the scene to assess the scope of the damage. Officials here in the city have been left to coordinate the efforts and any donations that will come in from the public.

“The international response is overvalued in these first days,” Mr. Egeland said. “The local response is undervalued. What has been done by local municipalities and local NGOs has been remarkable.”

Still, local relief organizations have begun to set up hotlines and mailboxes to receive donations. Groups based in the city, including the American Red Cross in Greater New York, the American Jewish Joint Distribution Committee, and Action Against Hunger, are ready to accept donations.

A spokesman for Action Against Hunger, John Sauer, said the organization plans to send more people to other affected countries as it receive more reports from ground sources.

“We are accepting donations to help the victims and we will be maintaining our activities in Sri Lanka,” he said. “We are concerned about the overall food situation, not only because of the tsunami, but also before it hit there has been flooding already and 75% of the harvest has been hit. So there was already a crisis and now the crisis is being compounded.”

He estimated that at least 225,000 people in Sri Lanka alone would be affected.

In addition to private organizations’ efforts, a $15 million aid package has been offered by the American government to the Asian countries, including $4.4 million of a $6.6 million appeal by the Red Cross from the world community. The 25-nation European Union has pledged $4 million.

The humanitarian group Doctors Without Borders has already received calls to its New York office, which coordinates the group’s projects overseas, from physician volunteers offering to assist in the relief effort.

The group’s teams in Australia and Japan will be first to the front lines of the relief effort. Teams of doctors were already working on AIDS and malaria health projects in the affected countries before the tsunami hit.

“They will very quickly switch gears and do a quick assessment of the needs, whether it’s blankets, sanitation, water, or food,” the group’s communications director, Kris Torgeson, said. “Right now we are in the full-force assessment mode.”