A graphic with map of Asia summarising the destruction wrought by the earthquake and tidal wave.(AFP)

The world's biggest earthquake in 40 years on Sunday hit southern Asia, unleashing a tsunami that crashed into Sri Lanka and India, drowning thousands and swamping tourist isles in Thailand and the Maldives.

A wall of water up to 10 meters high triggered by the 8.9 magnitude earthquake swept into Indonesia, over the coast of Sri Lanka and India and across southern Thai touristislands, leaving more than 6,300 feared dead in seaside towns and villages.

In Sri Lanka, where officials put the death toll at 2,200, the government appealed for emergency international assistance. Official figures suggested that one million people, or 5 percent of the population, were affected. Thousands fled the worst tsunamiin living memory, scrambling to higher ground for fear of another wave.

Two-thirds of the Maldives capital, Male, was flooded and officials voiced anxiety for the fate of dozens of low-lying, palm-ringed coral atolls crowded with international tourists for the Christmas holiday season.

India feared a devastating toll along its southeastern coast. In the state of Tamil Nadu alone, a government official said at least 1,873 had been killed. Rescuers were searching for hundreds of missing fishermen. Prime Minister Manmohan Singh put the armed forces on alert.

Some 5,000 Tamil Nadu fishermen went missing Sunday following atsunami in the Bay of Bengal triggered by a massive earthquake in Indonesia, local police said.

Indo-Asia News Service quoted the police in Chennai, capital city of Tamil Nadu, as saying that some 5,000 fishermen from the state were out at sea when the tidal waves struck and there has been no word of them so far.

Most of those who died onshore were children and elderly peoplecaught unawares as the rising waters inundated their shanties on the coastline.

The earthquake of magnitude 8.9 as measured by the US Geological Survey first struck at 0059 GMT off the coast of the northern Indonesian island of Sumatra and swung north with multiple tremors into the Andaman islands.

In Thailand, at least 223 people had been killed and more than 1,000 injured, officials said.

In the popular holiday islands off southern Thailand, rescue workers extracted about 70 Thai and foreign divers from the famed Emeral Cave and several dozen were found and evacuated from aroundother islands, officials said.

"Nothing like this has ever happened in our country before," said Thai Prime Minister Thaksin Shinawatra.

Reports said the earthquake was the world's biggest since 1964 and the fifth-largest earthquake since 1900.

Maldives was declared state of emergency after a national disaster in the island nation whose coral atolls are a magnet for tourists from around the world.

The world's worst tsunami in recent history struck on July 17, 1998, when three waves ripped through Papua New Guinea's northwestcoast, killing 2,500.