The death toll from floods and landslides following cyclonic rains in the Indonesian island of Sumatra has risen to 303, the head of the country's disaster mitigation agency said on Saturday, up from a previous figure of 174 dead.

Rescuers are searching in rivers and the rubble of devastated villages for bodies and possible survivors after floods and landslides on Indonesia’s Sumatra island.

The death toll from devastating floods and landslides in Southeast Asia climbed past 400 on Saturday as clean-up and search-and-rescue operations got underway in Indonesia, Thailand and Malaysia.

It is exceptionally rare for cyclones to happen in Indonesia, as they almost never form near the equator, says Erma Yulihastin, a researcher at the country's National Research and Innovation Agency’s Climate and Atmospheric Research Center (BRIN).