The National Building Research Organisation (NBRO) alerted the public to be vigilant on possible landslides in mountainous areas in Galle, Kegalle, Ratnapura, Kalutara, Matara and Hambanthota districts, Colombo Page reported.
Heavy rains have lashed several parts of the country since Thursday.
South-west monsoon conditions are establishing over the country. Hence, showery and windy condition are expected to continue over the south-western part of the country.
According to the Disaster Management Center (DMC), 23 people have died and over a million people have been affected due to the island-wide inclement weather.
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The DMC said water levels of most rivers were rising. It advised residents to take adequate measures to face a major flood situation.
Sri Lanka Airforce and the Navy are working to provide relief to people stranded by floods with helicopters and boats deployed, an official said.
Sri Lanka, which has been heavily deforested for cash crops, often witnesses landslides during the monsoon season.
Last year more than 100 people were killed in a massive landslide in the country.