Sri Lanka has been devastated, as surging waves from the Indian Ocean crashed into its eastern and southern coasts, and flooded vast areas Sunday morning.
Within hours of the tidal wave, the government in Colombo declared a national disaster, and appealed for international help.
In Maldives, nearly two-thirds of the capital, Male, was flooded, as a wave of water swept over the popular tourist destination. The international airport was shut on the island that lies just one meter above sea level.
The coasts of southern and eastern India were also hit. The state Tamil Nadu was the worst affected, with hundreds of people reported dead.
India's oil minister, Mani Shankar Aiyer, who is supervising relief operations, says initial reports suggest there is extensive damage in fishing harbors.
He says the damage is considerable, but it will take some time before they have an accurate picture.
The region was also rocked by tremors for hours after the massive earthquake hit off Indonesia. The most powerful tremor shook India's Andaman and Nicobar Island, destroying road and buildings.
Television footage here in India shows people crying and stunned, as they were taken to hospital after suffering injuries, many as they fled panicked from their homes.
Prime Minister Manmohan Singh has promised assistance to neighboring Sri Lanka. Relief operations have been ordered.
"I have also instructed the defense minister and home minister to take necessary measures by providing adequate relief and rescue," he said. "The paramilitary, as well as the armed forces, have been alerted, and are already in operation."
B. Lal, with the Indian Meteorological Department, says the effect of tidal waves lasts for many hours.
Mr. Lal says fishermen have been warned to stay off the coastal waters for at least two days. He also warns that tremors could continue to rock the region.