Nine people were killed after flooding and a landslide hit Indonesia's Sumatra island, an official said on Sunday.

"Heavy rains from Saturday evening till night triggered a landslide in the hilly area of Berastagi sub-district in North Sumatra," National Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said.

"Nine people were killed," he said, including four children aged between two and 10.

Local military official Meyer Putong, who was involved in rescue operations, said nobody was reported missing.

"They lived close to the river so the rush of rain water last night broke the riverbanks. The victims were either buried under their houses or swept by the surging waters," he added.

Indonesia is regularly affected by deadly floods and landslides during its wet season, which lasts for around six months.

Environmentalists blame logging and a failure to reforest denuded land for exacerbating flooding.