Hundreds of thousands of Sri Lankans abandoned their flooded homes and fled to higher ground on Sunday after the worst tsunami in living memory swamped the island’s south and east, killing more than 3,500 people. Government officials estimate 7,50,000 have been left homeless, many taking shelter in schools and temples, and said the final death toll could be much higher as hundreds washed out to sea have not yet been accounted for. Witnesses in this small fishing town near Colombo said giant waves crashed ashore on Sunday morning, sending a deluge of sea water into towns and villages. ‘‘A wave up to 10 ft in height hit this area and everything was swept away, including my three-wheeler taxi,’’ said 40-year-old fisherman Piyasoma. In Kalutara, holiday-makers at a hotel on the seafront described how they saw a 2.5 m wall of water crash onto the coast. ‘‘We were sitting on sunbeds when people started shouting a wave was coming in,’’ said British car salesman Richard Freeman. Many hotels along the southern tourism belt — jam-packed at the height of a bumper tourist season — were flooded. A French tourist in the southern town of Tangalla said his daughter had been swept away. Doctors evacuated pregnant mothers from maternity wards near Galle, as others fled houses submerged under several metres of muddy water. Witnesses saw corpses floating in flood waters, while thousands fled their homes in the hard-hit eastern Port of Trincomalee as cars floated out to sea. The tsunami was triggered by an 8.9 magnitude earthquake off the Indonesian island of Sumatra that was followed by a series of aftershocks stretching North into the Andaman Sea. Waves up to 15 feet high crashed onto Sri Lanka’s eastern and southern shores, flooding vast tracts of land and prompting President Chandrika Kumaratunga to declare a national disaster. ‘‘I think this is the worst ever natural disaster in Sri Lanka,’’ said N.D. Hettiarachchi, director of the National Disaster Management Centre. Swells soaked coastal areas in the Tamil Tiger rebels’ northeastern stronghold, an area still recovering from flooding from monsoon rains a fortnight ago that forced 250,000 people from their homes. —Reuters