Around 4,42,299 people belonging to 1,14,124 families were affected in 15 districts due to the flood situation, the Disaster Management Centre said today.
According to the Centre, 146 people were killed and 112 remained missing while 1,01,638 people belonging to 24,603 families were shifted to 319 safe locations.
"Although the heavy rainy condition has reduced temporary, showery conditions are likely to enhance again over south-western part of the island from 29th May 2017," the Meteorological Department said.
The fishing community in the country have been alerted about the condition.
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Sri Lanka's tri-forces personnel including more than 1,000 Army troops were engaged in the rescue and relief operations.
Meanwhile, Ministry of Foreign Affairs in coordination with the Ministry of Disaster Management, appealed to the United Nations, International Search and Rescue Advisory Group (INSARAG) and neighbouring countries to provide assistance to affected people, especially in the areas of search and rescue operations.
India was the first country to respond yesterday to the grave situation and it dispatched three Navy ships with emergency supplies to help Sri Lanka in the rescue and relief operations.
Other Indian ship -- INS Shardul reached Colombo today with relief materials. A third ship -- INS Jalashwa has also left for Sri Lanka.
The flooding is the worst since May 2003 when 250 people were killed and 10,000 homes destroyed after a similarly powerful Southwest monsoon, officials had said.
Last year, more than 100 people were killed in a massive landslide in the country.