As many as 112 people are still missing, and the death toll is expected to rise, as authorities battle to rescue those still stranded and warn of the possibility of crocodile attacks.
"It was only the next morning that troops arrived in boats, and took us to safe ground," Banakiyanage Gnanawathie, who lives in the badly hit town of Matara, told CNN by phone.
"I have never seen such floods though I have spent my entire lifetime in Matara. We have lost all our belongings and remain in the clothes we wore. I am still happy we escaped the floods and even the crocodiles," she said.
She said that they won't be able to return home for days.
"There is only a roof and building. We have lost everything else."
The heavy rain occurred over a very short period of time, leading to the displacement of 112,000 people, according to Pradeep Kodippily, spokesman for Sri Lanka's Disaster Management Center. Almost half a million people have been affected by the flooding.
The bout of severe weather has also triggered landslides throughout the country.
The southern coastal city of Galle has seen 223 millimeters (8.78 inches) of rainfall over the past 48 hours, and Ratnapura, further inland, has experienced 453 millimeters (17.8 inches) of rain over the same period.
Police and military rescue teams are moving by boat to rescue those marooned as well as retrieve corpses.
Houses and shops remain submerged in ten to thirty feet of water. The expressway from Colombo to Matara, 100 miles south of the capital, remains flooded in several areas.
'We could not stand up'
Stonemason Kirindagamage Pathmasiri, another Matara resident, said that the police had urged people to evacuate, but he and his family stayed put as they had nowhere to evacuate to.
"The next day the waters began to rise gradually. Then the flow was so fast that we could not stand up. My wife, four children and I were very frightened. We did not know what would happen to us now. With great difficulty we managed to walk out," he said. They are taking temporary shelter in a school.
He said that his house is now submerged under eight feet of water.
"A bigger shock awaits us when the waters recede and we return home. We have lost all our possessions," he said.
Sri Lanka's Ministry of Foreign Affairs activated its Emergency Response Unit and called on the United Nations' International Search and Rescue Advisory Group, as well as neighboring countries, to help in the recovery effort. The government has deployed 2,000 military personnel to affected areas.
India has dispatched three naval vessels to its southern neighbor to deliver relief aid and disaster expertise.
"Prime Minister Narendra Modi immediately directed provision of all necessary assistance," a statement issued by High Commission of India, Colombo, read.
"He also expressed condolences at the loss of lives and property and said that India stands with her Sri Lankan brothers and sisters in their hour of need."
The navy's official twitter handle posted media of one of the vessels, INS Shardul, docking in Colombo and unloading aid Sunday. It joins the INS Kirch, and a larger vessel, INS Jalashwa, will arrive within the next two days.
The country's High Commission in Colombo tweeted images of "Indian diving and medical teams deployed at Kalutara, Ratmalana (and) Galle with (Sri Lankan) navy relief (operations)."
The High Commission also tweeted an image of the Sri Lankan foreign minister, Ravi Karunanayake, receiving aid from one of the Indian vessels.
"Several countries have responded so far to Sri Lanka's request," Karunanayake told CNN, including Russia and China.
"The World Food Program is also providing help," he said.
Last year, India sent two ships and Air Force aircraft to Colombo with relief items during a cyclone.
"We have a problem of limited resources to cope with the situation," Karunanayake said. "Hence we have made many appeals."
A Sri Lanka Air Force troop transport helicopter had to make a forced landing into flood waters at Baddegama, near Galle.
"They were on a rescue operation and had no place to land due to a technical glitch," Air Force Commander Air Marshal Kapila Jayampathy told CNN.
ideo images from the Asiavision Sri Lanka news exchange showed people in streets wading through water that was shoulder-deep in some places. Others showed earthmoving equipment clearing mounds of dirt in areas where landslides had blocked roads.
The monsoon rains are the the worst to hit Sri Lanka since 2003. They come after two months of drought, which had grown severe enough to warrant aid from the World Food Programme.