(CNN) -- Massive tsunamis triggered by the largest earthquake to shake the planet in more than 40 years wiped out coastal areas across Southeast Asia as far as 1,000 miles away, killing more than 4,700 people.
Most of the deaths were in Sri Lanka and India.
The initial quake, measuring 8.9 in magnitude, struck about 100 miles (160 km) off the coast of Indonesia's Sumatra island around 7 a.m. Sunday (0000 GMT), according to the U.S. Geological Survey's National Earthquake Information Center.
It is the fifth largest earthquake in recorded history, according to the NEIC. The measurements have been taken since 1899.
Sri Lankan military authorities are reporting more than 2,400 people killed, most of them in the eastern district of Batticaloa. Several districts in the country's south have still not reported casualty figures, and authorities fear the death toll could rise.
Officials said thousands were missing and more than a half million had been displaced.
The huge waves also swept away a high security prison in Matara, in southern Sri Lanka, allowing 200 prisoners to escape. Eyewitnesses in the eastern Sri Lankan port city Trincomalee reported waves as high as 40 feet (12 meters), hitting inland as far as half a mile (1 km).
Sri Lankan officials imposed a curfew as night fell, and tourists were being evacuated from the eastern coasts to the capital, Colombo, which is on the west coast and was unaffected.
India agreed to assist Sri Lanka, sending two naval ships to the resort town of Galle, in the south, and Trincomalee, according to Colombo officials.
Indian aircraft will bring in relief supplies to the country on Monday.
India itself is reeling from the aftermath of the quake and tsunamis. Indian officials said at least 1,800 Indians were killed as a result of the massive waves. A resident of Chennai (formerly Madras) in Tamil Nadu district -- the hardest hit area -- said he witnessed several people being swept away by a tidal wave.
Along India's southeastern coast, several villages appeared to have been swept away, and thousands of fishermen -- including 2,000 from the Chennai area alone -- who were out at sea when when the massive waves swept across the waters have not returned.
Along the coast, the brick foundations of village homes were all that remained.
Interior Minister Shivraj Patil told CNN 700 people were killed in Tamil Nadu state and 200 in Andhra Pradesh. Poor communications with India's remote Andaman and Nicobar islands, which were closer to the quake's epicenter, has prevented any reports of damage and casualties. Most of the aftershocks have been centered off those islands.
Thai authorities say more than 300 are feared dead, and hundreds are missing. One witness said Phuket's famed Laguna Beach resort area is "completely gone." The area provides 40 percent of Thailand's $10 billion annual tourist income.
Among the missing were a number of scuba divers exploring the Emerald Cave off Phuket's coast.
Phuket's airport -- which closed down when its runways flooded -- reopened, but most roads remained closed, as officials tried to assess the damage, fearing structural damage to buildings closer to the shore.
Thai Prime Minister Thaksin Chinnawat arrived in Phuket and said the situation was "under control." He told CNN he planned to stay the night and direct rescue and relief efforts.
Eyewitnesses reported people drowning in their hotel rooms near the coast as 30-foot waves washed ashore. Others reported narrow escapes -- including one man whose alert but screaming boat driver turned their boat directly into a nearby shore. As he and his passengers scrambled up the steep beach, the waves crushed their boat.
More than 500 people were killed in Indonesia by the quake and the following tsunamis -- many of them in Aceh, in northern Sumatra, about 100 miles from the quake's epicenter, according to local reports.
"We still haven't got any reports from the western coast of Aceh, which is closest to the epicenter, so officials are bracing themselves for a lot more bad news," said journalist John Aglionby in Jakarta.
The earthquake is classified as "great" -- the strongest classification given by the NEIC.
NEIC geophysicist Don Blakeman said all of the tsunamis were triggered by the initial quake. Waverly Person, Blakeman's colleague at NEIC, said the tsunamis are "long over at this point," and residents and visitors should not be concerned with more high water.
One major aftershock, measuring 7.3 in magnitude, struck about 200 miles (300 km) northwest of Banda Aceh -- on Sumatra's northernmost tip -- over four hours after the initial quake, according to the NEIC. The rest of the aftershocks measured under 6.5 in magnitude.
The NEIC 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," he said.
He explained the quake was the energy released from "a very large rupture in the earth's crust" over 600 miles (1,000 km) long. The rupture created shockwaves that moved the water along at several hundred miles per hour.
It was the strongest earthquake to hit 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.
for those of you who have little/no idea how the richter scale works:
code:Richter TNT for Seismic Example
Magnitude Energy Yield (approximate)
-1.5 6 ounces Breaking a rock on a lab table
1.0 30 pounds Large Blast at a Construction Site
1.5 320 pounds
2.0 1 ton Large Quarry or Mine Blast
2.5 4.6 tons
3.0 29 tons
3.5 73 tons
4.0 1,000 tons Small Nuclear Weapon
4.5 5,100 tons Average Tornado (total energy)
5.0 32,000 tons
5.5 80,000 tons Little Skull Mtn., NV Quake, 1992
6.0 1 million tons Double Spring Flat, NV Quake, 1994
6.5 5 million tons Northridge, CA Quake, 1994
7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon
7.5 160 million tons Landers, CA Quake, 1992
8.0 1 billion tons San Francisco, CA Quake, 1906
8.5 5 billion tons Anchorage, AK Quake, 1964
9.0 32 billion tons Chilean Quake, 1960
10.0 1 trillion tons (San-Andreas type fault circling Earth)
12.0 160 trillion tons (Fault Earth in half through center,
OR Earth's daily receipt of solar energy)
160 trillion tons of dynamite is a frightening yield of energy. Consider, however, that the Earth receives that amount in sunlight every day.