The north-central province of Polonnaruwa, which borders territory controlled by Tamil Tiger rebels and has some of Sri Lanka's finest ancient ruins, was worst affected.

"We issued a warning on Wednesday to residents living near Kaudulla tank in Polonnaruwa to evacuate immediately as the tank is on the verge of overflowing," said National Disaster Management Centre Director N.D. Hettiarachchi, referring to the reservoir.

The Meteorology Department has forecast more rains over the next few days, but said the worst appeared to be over. However, a new weather system over the Bay of Bengal could bring more rains later in the week, the department said.

Floods are common across Sri Lanka during the north-east monsoon from December to January, and strand tens of thousands of people each year. In May 2003, flash floods in the south of the Indian Ocean island killed 250 people and left 500,000 homeless.

Sri Lanka has been hit by cyclical floods and droughts in recent years. A drought earlier this year left more than 200,000 people without drinking water, ravaged crops and affected nearly 10 percent of the 19 million population.