CHENNAI, India (CNN) — The death toll from Sunday’s tsunamis climbed to 21,000 by Monday as fears of disease from decaying bodies and contaminated water grew in Indonesia, India, Sri Lanka and Thailand.
The giant waves — triggered by the most powerful earthquake on Earth in 40 years — also left thousands injured, thousands missing and hundreds of thousands homeless.
A Sri Lankan forecaster warned of a “remote possibility of small tidal waves” caused by aftershocks Monday.
Some of the tsunamis reached as far as 1,000 miles from the epicenter of the 9.0 magnitude quake, which was located about 100 miles (160 km) off the coast of Indonesia’s Sumatra Island at a depth of about 6.2 miles (10 km).
The quake struck about 7 a.m. Sunday (7 p.m. ET Saturday), according to the U.S. Geological Survey’s National Earthquake Information Center (NEIC). It is the fourth-largest earthquake since such measurements began in 1899, according to the NEIC, tying a 1952 quake in Kamchatka, Russia.
More than 10,000 people have been reported dead in Sri Lanka. Most of them, authorities said, were in the eastern district of Batticaloa. Thousands were missing, an estimated 1 million were displaced and an estimated 250,000 were homeless.
In southern Sri Lanka, 200 prisoners escaped when the waves swept away a high-security prison in Matara.
Witnesses in the eastern Sri Lankan port city of Trincomalee reported 40 foot (14 meter) waves hitting inland as far as a half mile (1 km).
The Sri Lankan government declared a state of emergency, and, along with the government of the Maldives, has requested international assistance, the U.N. Office for the Coordination of Humanitarian Affairs reported.
As the sun rose, 20,000 Sri Lankan soldiers and naval personnel launched relief and rescue efforts. India sent six warships carrying supplies, along with helicopters. Priorities included identifying the hardest-hit areas and airdropping supplies, along with shepherding stranded people to safer areas.
Sri Lankan authorities imposed a curfew overnight, and many residents remained concerned about the possibility of additional tsunamis. The country has been in the throes of a civil war, and land mines uprooted by the waves were hampering relief efforts.
Sri Lanka’s director of meteorology Abey Singha Bandara told CNN his department’s analysis suggested “a remote possibility of small tidal waves, but not of the magnitude experienced on Sunday.”
Some tourists, meanwhile, were evacuated from the hard-hit eastern coasts to the capital Colombo, on the west coast and unaffected by the disaster.
At first light, many Sri Lankans ventured out to scour the debris for belongings or to search for information on missing family members.
In India, the official government news agency Press Trust of India said at least 6,200 Indians were killed, and more bodies were being recovered.
A resident of Chennai (formerly Madras) in Tamil Nadu district — India’s hardest-hit area — said he saw several people being swept out to sea.
Along India’s southeastern coast, several villages appeared to have been swept away. Thousands of fishermen — including 2,000 from the Chennai area alone — who were at sea when the waves thundered ashore have not returned.
Along the coast, brick foundations were all that remained of village homes. In Tamil Nadu, 2,500 people have been confirmed dead, and officials said 3,000 died on the remote Andaman and Nicobar islands, where dozens of aftershocks were centered. Communication from the islands to the mainland was cut off.
In Thailand, authorities said at least 866 people are dead, and hundreds are missing. Among the missing were scuba divers who had been exploring the Emerald Cave off Phuket’s coast.
Phuket’s airport — which closed when its runways flooded — reopened, but most roads in the area remained closed as officials tried to assess the damage.
Thai Prime Minister Thaksin Shinawatra arrived in Phuket and declared the situation “under control.” He told CNN he planned to direct rescue and relief efforts overnight.
Witnesses reported guests drowned in their hotel rooms near the coast as 30-foot waves washed ashore.
Others reported narrow escapes, including a Spaniard who had been aboard a boat when a wave approached.
The captain began screaming and turned the boat directly into a nearby shore, where he beached it. As those aboard jumped from the craft and scrambled up the steep beach, they turned back to see the waves crush their boat, the Spaniard said.
Among the dead are six Americans — five in Sri Lanka and one in Thailand, U.S. officials said. A number of Americans also were injured in Thailand.
More than 4,350 people are reported dead in Indonesia — many of them in Aceh in northern Sumatra, about 100 miles from the quake’s epicenter, officials said.
The quake also inflicted heavy damage on the area, which is a hotbed of rebel activity, before two tsunamis slammed the coastline. Access and communications were difficult if not impossible. The death toll remained a mystery on the west coast of Aceh, where communication had been wiped out.
In the Maldives, 46 people are dead and more than 70 missing, according to Hassan Sobir, the Maldives High Commissioner.
The tsunamis struck with no warning to those in coastal areas, as no warning system exists for the Indian Ocean, said Eddie Bernard, director of the U.S. National Oceanic and Atmospheric Administration’s Pacific Marine and Environmental Labs in Seattle.
Staffers at warning centers that cover the Pacific Basin and the U.S. West Coast were aware of the quake and the possibility of tsunamis, said Laura Kong, director of the International Tsunami Information Center in Honolulu, Hawaii.
“They were able to make contact, but they did not have the proper government officials to notify,” she said. “They’ll be working on this in the future.”
The earthquake is classified as “great” — the strongest classification given by the National Earthquake Information Center.
NEIC geophysicist Don Blakeman said the tsunamis were triggered by the initial massive jolt.
“The damage is just phenomenal,” said Jan Egelund, U.N. emergency relief coordinator. “I think we are seeing now one of the worst natural disasters ever.”
There was disagreement over whether the threat was over. Waverly Person, Blakeman’s colleague at NEIC, said the tsunamis are “long over” and residents and visitors should not worry about further tsunamis.
Bernard, however, said the aftershocks are strong enough to produce more tsunamis.
One such aftershock, measuring 7.3 in magnitude, struck about 200 miles (300 km) northwest of Banda Aceh — on Sumatra’s northernmost tip — more than four hours after the initial quake, according to the NEIC. The center expects the quake to produce hundreds of smaller aftershocks under 4.6 magnitude, and thousands smaller than that.
“A quake of this size has some pretty serious effects,” Person said.
The quake represented the energy released from “a very large rupture in the earth’s crust” more than 600 miles (1,000 km) long. The rupture created shock waves that pushed the water at speeds of up to several hundred miles per hour.
It was the strongest earthquake to hit anywhere on Earth since March 1964, when a 9.2 quake struck near Alaska’s Prince William Sound. The strongest recorded earthquake registered 9.5 on May 22, 1960, in Chile.
Sunday’s quake hit a year after a 6.6-magnitude quake in Bam, Iran, killed more than 30,000 people, injured another 30,000 and destroyed 85 percent of the buildings in the southeastern Iran city.