Dec. 28 (Bloomberg) -- The United Nations said 24 countries have joined ``an enormous relief effort'' following a 9.0 magnitude earthquake off Indonesia's coast that killed more than 23,000 and destroyed towns from Thailand to India. Aftershocks may cause further tsunamis and flooding, officials said.

Damage from the earthquake, the world's biggest in four decades, ``will probably be many billions of dollars,'' said Jan Egeland, the UN's head of humanitarian affairs. Insurers' losses may be less than $5 billion because so little property in the region is insured, according to Robert Hartwig, an Insurance Information Institute economist in New York.

``This is not the biggest earthquake in recorded history, but the effects may be the biggest because many more people live in exposed areas than ever before,'' Egeland told reporters in New York. ``Hundreds of thousands of people have lost everything and millions have only polluted water to drink, no sanitation or health services.''

Egeland said more than 2,000 UN workers and hundreds of airplanes will arrive within 48 hours in the eight nations most severely affected by the earthquake off Sumatra. The International Federation of Red Cross and Red Crescent Societies asked for $6.6 million in emergency aid and the World Food Program appealed for $1.5 million.

Australia has sent two military planes to Malaysia to ferry emergency supplies such as bottled water and tarpaulins to the affected countries, Prime Minister John Howard told a press briefing.

Aid Donations

The U.S. plans to give $15 million, Secretary of State Colin Powell told reporters in Washington. The European Commission said it will donate up to $30 million to aid people in the affected areas, on top of $3 million it allocated to the Red Cross yesterday. Australia's government said the nation will give $7.7 million to the quake zone.

Yesterday's quake generated waves as high as 10 meters (33 feet), striking tourist resorts in Thailand and the Maldives. Sri Lankan police reported about 10,000 dead, while Indonesia said at least 4,491 were killed, prompting governments in the two countries to declare national disasters.

``The reports from individual countries we are getting add up to more than 23,000 dead, and I think it may actually turn out to be two or three times that.'' the UN's Egeland said.

Aftershocks

In the two hours following yesterday's earthquake, there were 25 aftershocks, the U.S. Geological Survey reported.

Aftershocks may continue for ``weeks rather than days because it's such a major event,'' said Vasily Titov, a tsunami research scientist at the U.S. Government's National Oceanic & Atmospheric Administration. ``There is potential for an earthquake with a magnitude of 8.0 or so as an aftershock.''

A tsunami last crossed the Indian Ocean in 1509, Titov said. Scientists and governments had not expected anything close to the earthquake and freak waves that hit Asia yesterday, because 90 percent of tsunamis occur in the Pacific Ocean, where sophisticated alert systems are in place.

``We were bracing for an event like that in the Pacific, but it happened in the Indian Ocean where the infrastructure for tsunami warnings systems is pretty much non-existent,'' Titov said in a telephone interview from the Seattle-based Pacific Marine Environmental Laboratory.

Receding Water

The earthquake was centered 1,605 kilometers (1,000 miles) northwest of Indonesia's capital, Jakarta, at a depth of 10 kilometers, the U.S. Geological Survey said.

``The sad thing is that the devastation could have been easily prevented if people were just a little bit educated about what to do,'' Titov said. ``Instead of following the receding water down to the open ocean, they should have taken it as a sign to escape from the coast. People just didn't know.''

The Indian government said at least 4,000 people have died. Another 6,000 are missing in the Andaman and Nicobar islands, Finance Minister P. Chidambaram said in New Delhi today. More than 3,000 people have died in the Indian islands of Andaman and Nicobar, Press Trust of India reported, citing S.B. Deol, inspector general of police.

In Thailand, where the tsunamis struck during what is the country's peak tourist season, ``people turned up at the hospital just in their bathing costumes with no shoes, possessions or money,'' said Tiyanooch Ananpakdee, communications manager for Bangkok Phuket hospital, via telephone from Phuket.

Foreign Tourists

More than 95 overseas tourists died in Thailand and Sri Lanka, while 530 Japanese travelers are missing, according to tallies from foreign embassies.

As many as 10,000 Britons may be in the region, the Association of British Travel Agents said, and the travel company TUI AG said it has about 2,000 German tourists there. Australia's Prime Minister Howard said about 5,500 of the country's citizens are holidaying in the affected countries.

Powell said 8 U.S. citizens were known dead and that several hundred are unaccounted for. The U.S. State Department urged Americans to avoid traveling to Sri Lanka or the Maldives, and asked U.S. citizens living in the two countries to register with their embassies.

European travel companies including Thomas Cook AG, TUI and Club Mediterranee SA canceled trips and have begun bringing customers home. Star Cruises Ltd., the world's third largest cruise ship operator, said in an e-mailed statement it had canceled cruises planned between Singapore and Phuket.

Thai Airways International Pcl, Thailand's biggest carrier, and Malaysia's AirAsia Bhd have resumed flights after canceling services when Phuket airport was forced to close at 11:30 a.m. Dec. 26. It resumed services at 5 p.m.

1964 Quake

The quake is the biggest since 1964, when a 9.2 magnitude temblor hit Prince William Sound in Alaska, according to the U.S. Geological Survey. The strongest since 1900 was a 9.5-magnitude earthquake in Chile in 1960. More than 41,000 people died when an earthquake measuring 6.6 devastated the Iranian city of Bam on Dec. 26, 2003.

The Indonesian quake is the second in the world this year of magnitude 8 or greater on the Richter scale. A magnitude 8.1 temblor was recorded on Dec. 24 in the Southern Ocean between Australia and Antarctica by the U.S. Geological Survey.

Magnitude 8 earthquakes are capable of causing severe loss of life if centered near heavily populated areas. An 8.1 quake in Mexico City in 1985 killed about 9,500 people.

To contact the reporters on this story: Bill Varner at the United Nations at wvarner@bloomberg.net Beth Jinks in Singapore at at bjinks1@bloomberg.net

Last Updated: December 27, 2004 15:49 EST