The death toll from devastating floods and mudslides in Sri Lanka has exceeded 330 people, as the country grapples with one of its worst weather disasters in years.

More than 200 are missing, and some 20,000 homes have been destroyed, sending 108,000 people to state-run temporary shelters, the Disaster Management Centre reported.

Officials said that about a third of the country was without electricity or running water as a state of emergency was announced in the aftermath of Cyclone Ditwah.

President Anura Kumara Dissanayake said it is the "most challenging natural disaster" in the country's history, and that the destruction was so severe that estimates for reconstruction were staggering.

Evacuation orders are in place in some areas as water levels of the Kelani River continue to rise rapidly.

A woman from central Sri Lanka told the BBC that about 15 houses in her area were buried under boulders and mud. None of the residents survived, she said.

The highest number of deaths was reported in Kandy and Badulla, where many areas remain cut off.

"We lost two people in our village... others are sheltering in a temple and a house that is still standing," said Saman Kumara from the Badulla village of Maspanna.

"We can't leave the village, and no one can come in because all roads are blocked by landslides. There is no food, and we are running out of clean water," he told the News Centre website by telephone.

Victims also include 11 residents of an elderly care home that was flooded in the north-central district of Kurunegala on Saturday afternoon, police said.

Speaking after the 24-hour rescue effort, one passenger told the AFP news agency how the navy had to help them climb onto the roof of a nearby building.

"We were very lucky... while we were on the roof, part of it collapsed... three women fell into the water, but they were helped back onto the roof," WM Shantha said.

The government has issued an appeal for international aid and urged Sri Lankans abroad to donate money to support affected communities.

Cyclone Ditwah brushed the island nation's eastern coast on Friday but has since moved away from the country.

Sri Lanka is currently experiencing its monsoon season, but it is rare for the island to see extreme weather on this level.

The worst flooding this century in Sri Lanka was in June 2003, when 254 people were killed, and hundreds of thousands were displaced.

The flooding comes as South East Asia is also facing some of the worst floods the region has seen in years, with millions impacted across Indonesia, Malaysia and Thailand.