Helicopters are searching for people marooned four days after rain-triggered floods and mudslides inundated Sri Lankan neighbourhoods and killed at least 164 people.
With more downpours expected on Monday, rescuers raced to evacuate people from the most vulnerable areas.
More than 100,000 people have already taken shelter in 339 relief camps set up in the country's south and west.
Army boats skimmed waterlogged village streets, while able-bodied victims waded through brackish waters to army trucks carrying relief supplies.
"We are displaced and have no place to go," said Rathana Kumari, who fled her home with her family and took refuge on the Southern Expressway, a major highway linking the commercial capital of Colombo with the cities of Matara and Galle.
"Now we are extremely helpless with our little children. Today, we didn't get anything to eat."
Officials say at least 104 people are missing after the floods hit on Friday along with cascades of red mud that swallowed village homes.
Special medical teams have been sent to affected areas, while medicine has been sent by air to hospitals unreachable by road, said Health Minister Dr Rajitha Senarathna.
Soldiers took advantage of a lull in the rain Sunday to clear roads to reach some affected areas, said Major General Sudantha Ranasinghe, who is heading the search and rescue mission.
The United Nations said it had joined the relief efforts and would donate water purification tablets, tents and other supplies.
India sent a shipload of goods, while the United States and Pakistan also promised relief supplies.
Mudslides have become common during Sri Lanka's summer monsoons, as forests across the tropical Indian Ocean island nation are cleared for export crops such as tea and rubber.
Another massive landslide a year ago killed more than 100 people in central Sri Lanka.