More than 2,000 people have died after huge waves swept into southern Indian states, following the world's most powerful earthquake for 40 years.
Air force helicopters have been pressed into service
The water took 1,705 people in the state of Tamil Nadu alone, officials say. Parts of Andhra Pradesh and Kerala were also struck.
Bodies are said to be strewn along the 2,000km (1,200-mile) coastline.
More than 300 people are also reported to have died on India's Andaman and Nicobar Islands, close to Indonesia.
In India, Prime Minister Manmohan Singh said he was deeply shocked by the devastation.
"My heartfelt sympathies are with the families of the bereaved, and with all those affected in our country," he said in a televised broadcast.
Early morning joggers along the Marina beach in the Tamil Nadu capital, Madras, say huge columns of water surged towards the land without warning.
The BBC's Sampath Kumar in the city says water came several kilometres inland.
A nuclear reactor in the state was shut down after sea water entered an estate housing scientists.
Sea water flooded the streets of Cuddalore, some 150km (90 miles) south of Madras, overturning several cars and leaving nearly 800 people dead.
Fishermen were swept off the sea
Indian air force helicopters have been despatched to evacuate people living in the submerged areas.
A rescue effort was also launched for 500 tourists reported to have been stranded on the Vivekananda rock memorial, a popular destination on an Indian Ocean island, a few kilometres off the tip of the mainland.
Casualty figures on India's Andaman and Nicobar Islands could not be officially confirmed, but a police chief told reporters 300 people had died and another 700 were feared dead.
The BBC's Geeta Pandey, who is in the regional capital Port Blair, says jetties on the island's main port have collapsed and many people have been forced out of their homes, which are flooded.
The main road on the highway is badly damaged with enormous gashes on its surface.
An islander, Kakoli Roy, wept as she surveyed her damaged home with most of her furniture and household belongings ruined beyond repair.
"This is our whole life's acquisitions gone in a second," she told the BBC.
"My husband retires from his job next year and we have no other source of income. I don't know what we'll do."
'Boats of paper'
More than 100 people have also died in Kerala, a key tourist destination on India's west coast.
In Andhra Pradesh state, more than 60 people are thought to have been killed.
A resident of Kakinada in the province, P Ramanamurthy, said he saw fishermen being swept out to sea.
"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," he told the Associated Press news agency.
"Many boats were upturned, but fishermen were still holding onto them," he said.
Tidal waves flooded the Vishakhapatnam port, one of the country's major shipbuilding centres.
The authorities there say army, navy and air force personnel have been called in to help with the rescue and relief operation.