The Disaster Management Centre (DMC) said the adverse weather condition had left 112 people injured and nearly 600,000 people have been forced from their homes, with thousands suffering structural damage from flood inundation and landslides.
State television broadcast called for public assistance to clean drinking wells contaminated by the monsoon floods.
Lanka's water supply minister Rauf Hakeem said 40 per cent of those affected did not have access to piped drinking water, and there was an urgent need to clean contaminated wells in flood-affected areas.
In total, 545,243 people of 142,811 families had been affected by the weather calamity. The South-West monsoon unleashed torrential rains, which ravaged fourteen districts in the western and southern parts of the country on Friday and Thursday.
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The disaster is described as one of the worst-ever calamities since the 2003 floods.
The official death toll was at 183, with another 110 people were listed as missing, the Daily Mirror reported.
The MeT Department in its weather forecast said the cyclonic storm MORA is expected to get weakened when it enters the Bangladesh land and the possibility for heavy rain and strong winds will be reduced by tomorrow.
The MeT Department warned that the sea area off the coast extending from Puttalam to Trincomalee via Kankasanthurai and sea area off the coast extending from Galle to Batticaloa via Hambantota can be very rough at times as the wind speed can increase up to 70-80 kmph.
There were scattered showers in many parts of Sri Lanka in the past 24 hours but flood waters were rapidly receding, officials said.
The DMC had issued an urgent evacuation warning last evening instructing residents living along the Kelani River and within the Divisional Secretariats of Kollonnawa, Kaduwela, Wellampitiya, Kelaniya, Biyagama, Sedawatte, Dompe, Hanwella, Padukka and Avissawella to move to safer areas.
It said water levels in the Kelani River were rising rapidly as indicted by the water gauges at Nagalagam Street, Hanwella and Glencourse and warned residents to move away from the vulnerable area as it was under an imminent flood threat.
Those living along the banks of Nilwala Ganga, The Gin Ganga and Kalu Ganga were also asked to move to safer areas because of the rising water levels.
Meanwhile, the DMC requested the people to be vigilant on rising water levels.
"Showers or thundershowers will occur at times in the Western, Sabaragamuwa, Southern, Central and North-western provinces. Heavy falls (about 150 mm) can be expected at some places," it said.
Sri Lanka has sought international assistance, with India sending two naval ships laden with supplies over the weekend.
Indian Navy diving and medical teams arrived in INS Shardul yesterday and have been deployed to assist Sri Lanka Navy operations at Kalutara, Ratmalana and Galle.
Following India's lead in sending out emergency relief to Sri Lanka, more countries have started pledging assistance to provide relief to the flood victims.