Over 2,400 people were killed when tsunamis, triggered by a massive earthquake -- 8.5 on the Richter scale -- that hit the Indonesian island of Sumatra, pounded more than half of Sri Lanka's coastlines on Sunday morning.

The government declared a state of disaster in the wake of the calamity as the casualty figures mounted and displaced people in the island's worst affected areas sought shelter in makeshift refugee camps.

More than a thousand perished in Batticaloa district alone, according to reports. In Trincomalee, there were reports of 320 deaths. The Galle tourist resort reported around 200 deaths.

Around 200 prisoners escaped when waves swept away a prison in Matara, in southern Sri Lanka.

Prime Minister Mahinda Rajapakse, whose office is coordinating the relief work, flew by helicopter to some of the most devastated regions.

"The devastation is massive. It is unprecedented. The prime minister has gone by helicopter to some of the areas which had been cut off," said Lalith Weeratunga, his aide.

"We are getting reports from the main towns, but there are still areas which have been cut off," he added.

President Chandrika Kumaratunga was expected back in Sri Lanka after cutting short a holiday in Britain.

Her office said she had issued an appeal for international aid to deal with the overwhelming disaster. The army, navy and air force were called out to help local officials and police in rescuing the marooned and providing food and medicine for the refugees, while police also declared local curfews in many areas to prevent looting of damaged hotels, homes and shops.

The PM urged India to provide urgent medical assistance to his country and help with helicopters in the rescue mission.

India agreed and sent two naval ships to Galle, in the south, and Trincomalee. Indian aircraft will bring in relief supplies to the country on Monday.