Fifteen students holidaying at a popular tourist spot in western Indonesia have been killed in a landslide, an official said Monday, with fears the death toll could rise.

Heavy rain and flash flooding triggered a major landslide Sunday at a famous "two-coloured" waterfall at Sibolangit in the north of Sumatra island, said disaster agency spokesman Sutopo Purwo Nugroho.

Searchers had so far unearthed 15 bodies, Sutopo said late Monday. Two others, presumed dead, were still being recovered, while four remained missing.

"It is believed those victims were also buried in the landslide," Sutopo said in a statement.

Fifty-seven others had been found alive with just one injured, he added.

About 300 people joined in the search, including students and volunteers.

The waterfall is reached after several hours' hike from a campground at Sibolangit. The forest getaway is highly popular at weekends and the victims were believed to be campers from several universities.

Landslides are not uncommon in Indonesia, a vast tropical archipelago prone to natural disasters and torrential downpours.

Nearly 100 people died in December 2014 when a landslide buried scores of homes on the main island of Java.