The National Building Research Organisation (NBRO), which monitors the stability of mountain slopes, said heavy rainfall within 24 hours could further saturate the hills and make them unstable.

"Since rainfall within the past 24 hours has exceeded 150 millimetres, if the rains continue, evacuate to a safe location to avoid the risk of landslides," the NBRO said in a statement.

The latest deluge was brought on by the onset of the northeast monsoon, though some of the earlier flooding that began last week has started to subside.

The Disaster Management Centre (DMC) said 486 people had been confirmed dead and another 341 were still unaccounted for.

The number of people in state-run refugee camps has dropped to 170,000 from a peak of 225,000 as floodwaters receded in and around the capital, Colombo.

Record rainfall had triggered the floods and deadly landslides, with President Anura Kumara Dissanayake saying it was the most challenging natural disaster to hit the island in its history.

Residents evacuated from the landslide-prone central hills have already been told not to return immediately to their homes, even if they were unaffected by the slips.

Friday's fresh landslide alert was issued for new areas that were not covered by previous warnings.

In the central town of Gampola, residents worked to clear mud and fix water damage.

"We are getting volunteers from other areas to help with this clean-up," Muslim cleric Faleeldeen Qadiri told AFP at the Gate Jumma Mosque.

"We have calculated that it takes 10 men a whole day to clean one house," said a volunteer, who gave his name as Rinas. "No one can do this without help."

- Troops back clean-up-

Sri Lanka's military said it had deployed thousands of troops in flood-hit areas to assist with the clean-up.

The top official in charge of the recovery, Commissioner-General of Essential Services Prabath Chandrakeerthi, said authorities were paying 25,000 rupees ($83) per home for cleaning, with reconstruction costs estimated at between $6-7 billion.

A further 2.5 million rupees ($8,300) is being paid to begin rebuilding destroyed homes. More than 52,000 houses had been damaged as of Friday morning, officials said.

Chandrakeerthi's office said nearly three-quarters of the electricity supply across the country had been restored, but some parts of the worst-affected Central Province were still without power and telephone services.

While the government has sought generous donations to recover from the massive loss of roads, bridges, homes and industries, tourism authorities said hotels were back in business.

Nearly 300 tourists who were stranded due to the disaster have been rescued by helicopter, the tourism ministry said.

"We need tourism revenues to help rebuild", Deputy Tourism Minister Ruwan Ranasinghe told reporters in Colombo.