Heavy rains in Sri Lanka have prompted devastating mudslides and flooding, killing at least 91 people and leaving more than 100 missing, according to authorities.

Search and rescue operations are currently underway, the Sri Lankan Disaster Management Center says.

Five rivers in the south and west of the island have flooded, affecting more than 61,000 people, the agency says.

The Associated Press reports that heavy rains are expected to continue, and that marooned victims are being rescued by helicopter and boat:

"Deputy Minister for Disaster Management Dunesh Kankanda said many people were on roofs and treetops calling for help."Many homes and roads were inundated. Schools were closed in the province of Sabaragamuwa, about 90 kilometers (55 miles) east of Colombo."Aid groups, rescuers and other government workers were ordered to cancel any holidays and remain on alert for the next three days."

A year ago, torrential rains in Sri Lanka triggered landslides that buried three villages. The mud was 30 feet deep in some areas, one rescue operator told Reuters at the time.

That disaster killed more than 100 people and completely destroyed more than 500 houses, AFP reported.

Sri Lanka's southwest monsoon season runs from May to September. But Reuters reports that recent rainfall has been unusually heavy, even for this rainy period.

"Sri Lankan meteorology officials said Thursday's rains are the worst since 2003," the wire service says.

And the AP notes that the region is increasingly vulnerable to rain-triggered landslides.

Copyright 2017 NPR. To see more, visit http://www.npr.org/.