The floods and landslides struck three districts in south-central Sri Lanka late Saturday after days of rain caused by a tropical depression in the Bay of Bengal. Previously, officials had said at least 200 people had died.
"The full extent of tragedy and loss of human lives are unfolding as we are reaching remote areas," rehabilitation minister Jayalath Jayawardene told The Associated Press.
Jayawardene said three relief teams have been sent to the worst affected areas and were reporting the new deaths.
"I appeal to international community to urgently help us with bottled water, shelter material, clothes and medicine," Jayawardene said.
Sri Lankan officials have said that another 200 are people are missing, including people buried by landslides. At least 60,000 houses have been damaged or destroyed in three districts.
Air force helicopters were ferrying water and food parcels — containing rice, curry, vegetables and chili paste wrapped in plastic and newspapers — to an estimated 150,000 people in affected areas across Sri Lanka.
Sri Lanka is a small tropical island with 18.6 million people off India's southern tip.