The Disaster Management Centre issued an urgent evacuation warning for residents living along the Kelani River and within the Divisional Secretariats of Kollonnawa, Kaduwela, Wellampitiya, Kelaniya, Biyagama, Sedawatte, Dompe, Hanwella, Padukka and Avissawella.
At least 200,382 people belonging to 52,603 families were affected in 14 districts. Further, 12,007 people belonging to 2,937 families were relocated to 69 safe locations as of Saturday morning, it said.
The death toll crossed 100 while 99 others were missing, officials said but did not provide the exact numbers.
A Sri Lanka Air Force (SLAF) airman died after falling from a helicopter during a flood rescue operation in Neluwa area in Galle.
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The Meteorology Department said that rain and windy conditions are expected to continue.
"Showers or thundershowers will occur at times in the Western, Sabaragamuwa, Southern, Central and North-western provinces," it said.
Sri Lanka's Ministry of Foreign Affairs in coordination with the Ministry of Disaster Management, appealed to the UN, 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.
The fist Indian navy ship with rescue and relief materials arrived this morning at the Port of Colombo.
Sri Lankan Foreign Minister Ravi Karunanayake, who was present to receive the ship, said: "We are grateful to India for sending relief at such a short notice so quickly."
He said India's move to send relief materials demonstrated the Indo-Lanka relations which are at an excellent level.
INS Kirch diverted to Colombo to render immediate assistance in flood relief operations, arrived in Colombo Port today. Indian High Commissioner Taranjit Singh Sandhu handed over the relief items brought by INS Kirch to Foreign Minister Ravi Karunanayake.
Medical and diving teams along with boats and helicopters are also being sent on board INS Jalashwa to assist Sri Lanka in rescuing people from flood-hit area, Indian Navy spokesperson Captain D K Sharma said.
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 said.
Sri Lanka's Ministry of Foreign Affairs said it had activated the Emergency Response Unit to coordinate rescue and relief measures related to the flood situation.
Last year, more than 100 people were killed in a massive landslide in the country.