Tourists, fishermen, hotels, homes and cars were swept away by walls of water unleashed by the 8.9-magnitude earthquake, centered off the west coast of the Indonesian island of Sumatra, where at least 1,870 people were killed by floods and collapsing buildings, officials said.
But the scope of the disaster became apparent only after waves as high as 20 feet crashed into coastal areas throughout the Indian Ocean and Andaman Sea.
In Sri Lanka — some 1,000 miles west of the epicenter — the death toll stood at 2,425, according to a military spokesman. One million more were affected by the surging wall of water, the government said.
Indian officials said as many as 1,130 had been killed along the southern coast. Another 198 were confirmed dead in Thailand, 42 in Malaysia and 2 in Bangladesh. Thousands of people were missing, many of them fishermen at sea, and rescue workers struggled against floodwaters to find and evacuate stranded victims.
The death toll climbed throughout the day and was expected to grow even higher as more bodies were discovered. Hundreds of bodies were found on various beaches along India's southern state of Tamil Nadu, and more were expected to be washed in by the sea, officials said.
"I was shocked to see innumerable fishing boats flying on the shoulder of the waves, going back and forth into the sea, as if made of paper," said P. Ramanamurthy, 40, a resident of the neighboring Indian state of Andhra Pradesh.
"Many boats were upturned, but fishermen were still holding on to them," Ramanamurthy said. "They also were pushed into the sea. It was shocking."
Among those killed along India's Andhra Pradesh state were 32 people, including 15 children, who had gone into the sea for a Hindu religious bath to mark the full moon day, police said. They said 20,000 people were evacuated in four districts.
The U.S. Geological Survey's Web site recorded the magnitude 8.9 earthquake off the west coast of northern Sumatra, 1,000 miles northwest of Jakarta. It was centered 25 miles below the seabed. Aftershocks struck in the magnitude 7 range.
The earthquake was the world's fifth most powerful since 1900 and the strongest since a 9.2 temblor slammed Alaska in 1964, U.S. earthquake experts said.
The force of it shook unusually far afield, causing buildings to sway hundreds of miles away, from Singapore to the city of Chiang Mai in northern Thailand, and in Bangladesh, hours after the region's Christian communities had finished Christmas celebrations.
Initial damage centered on the Indonesian province of Aceh on northern Sumatra. Dozens of buildings were destroyed, but as elsewhere, much of the death toll appeared to come from onrushing floodwaters.
Towns nearest the epicenter were leveled by tidal waves, which killed at least 1,870 people and left bodies wedged in trees as the waters receded, Indonesian officials and witnesses said. Officials warned the death toll could rise dramatically.
"I saw nine people killed by flooding, including four children," a witness who gave his name as Mustafa told el-Shinta radio station from Banda Aceh.
A spokesman for Indonesian state-owned Garuda Airlines said Banda Aceh's airport was flooded and planes were unable to land.
In Sri Lanka, the government called Sunday's events a national disaster and appealed for emergency relief.
"It is a very tragic situation," said police spokesman Rienzie Perera, adding that some hospitals were unable to treat the injured.
Holidays turned to disaster in southern Thailand, which welcomes hundreds of thousands of tourists to its southern beaches during the Christmas season. At least 198 people died, 1,900 others were injured and many more — reportedly including foreign tourists on diving excursions — were missing, authorities said.
"Just out of nowhere, suddenly the streets (were) awash and people just running and screaming from the beach," John Hyde, a vacationing Australian state lawmaker, told Australian Broadcasting Corp. television.
"People were getting swept along still on their motorbikes," Simon Morse, another Australian tourist, told the ABC. "There were cars that had been picked up by the storm surge and they were getting pushed down the road, taking things out as they went."
The owner of two resorts on Phi Phi island — where the Hollywood blockbuster "The Beach", starring Leonardo DiCaprio, was filmed — said that 200 of his bungalows were swept out to sea, along with some of his employees and customers.
"I am afraid that there will be a high figure of foreigners missing in the sea, and also my staff," said Chan Marongtaechar, who was in the Thai capital of Bangkok at the time. He estimated that 700 people could have been on the beach.
In India, the worst affected area was Tamil Nadu state, where 700-800 people are reported to have died, followed by Andhra Pradesh state where the toll was about 200.
At least 102 people were killed in the federally administered territory of Pondicherry near Tamil Nadu, Pondicherry Chief Minister N. Rangasamy said. At least 14 people were killed in Kerala state and 14 in Andaman and Nicobar Islands, Patil said.
Among those killed in Andhra Pradesh were 32 people — 15 of them children — who had gone into the sea for a Hindu religious bath.
"This is the impact of the earthquake in Indonesia this morning," said Andhra Pradesh Chief Minister Y. Raja Shekhar Reddy. "There were tidal waves in the sea and the entire coastal belt from Vishakhapatnam to Nellore (districts) has been affected."
High waves inundated the Maldives, a string of 1,192 coral atolls off the southwestern coast of India, injuring one Italian tourist and forcing the airport to close, an official said. A British man died from a heart attack minutes before the waves hit.
In Malaysia, authorities closed some beaches to the public after 42 people were swept away near the northern city of Penang. The victims were believed to be mainly tourists and included some foreigners, a police spokesman said. Their identities were not immediately known.
At least 2 children were killed when a boat capsized in Bangladesh, local authorities said.
Officials received reports that some vessels capsized at sea, but there were no further details, said Low Kong Chiew, director of the state government's Seismological Division.