Forecasters said more rain was on its way, which would make the plight of about 150,000 people left homeless even more difficult.
"It is a very grim situation," said rehabilitation minister Jayalath Jayawardene. "I have been told that at least 200 people have died and still there are people unaccounted for."
Prime Minister Ranil Wickremesinghe said the disaster was the nation's worst in five decades. The final death toll is "going to be heavy, sorry to say," he said without elaborating.
In Ratnapura, home to 1 million people, about 40,000 homes were damaged by the floods and landslides, forcing people to take shelter. Much of the area was without electricity and telephone service because the landslides damaged overhead lines.
Neighboring India was sending a rescue helicopter and a relief ship with medicine, food, water and health officials. It was expected to arrive later Monday, Indian High Commission spokeswoman Reenat Sandhu said in the capital, Colombo.
Norway also pledged $100,000 in emergency aid.
"I was very moved by witnessing the scope of the flood disaster and the plight of the flood victims," Norwegian Deputy Foreign Minister Vidar Helgesen said while visiting Sri Lanka.
The government already has appointed a four-member Disaster Management Ministerial Committee, allocated $62,500 for immediate relief and said it will pay $156 of the funeral expenses for each victim.
On Monday, tens of thousands of refugees housed in temples, schools and public buildings were being given buns, bread and sugar by volunteers and government's relief agencies.
Officials warned the flooding also could have a severe economic impact because the affected areas include dairy and rice farms that provide staple foods for many Sri Lankans. The floods have damaged many crops that already were harvested and stored.
The police chief in Ratnapura, Prasanna Nanayakkara, said road links with the capital were restored and water was receding from some areas.
He said about a dozen police teams have been dispatched to remote areas to look for survivors. Air force helicopters flew out of Ratnapura town to far-flung villages to look for survivors and to make food drops.
"It appears that the worst is over for now unless it rains again heavily," Nanayakkara said. "Light vehicles can now pass though there are patches where we still have mud and slit."
The Department of Meteorology warned of new rain Monday.
"There will be occasional showers accompanied by fairly strong winds," a department statement said.
The flash floods hit the area late Saturday evening after most residents returned to their homes from celebrating the island's biggest Buddhist festival marking the birth, death and enlightenment of Buddha.
Sri Lanka's Education Ministry said Monday it was postponing school examinations across the country.
Natural disasters of this magnitude are rare in Sri Lanka, a small tropical island country with 18.6 million people off India's southern coast.
On May 13, a cyclone hit the country and since then it has been raining heavily in central and southern parts of the country, caused by a tropical depression in the Bay of Bengal.
By Krishan Francis