A passenger boat believed to be carrying as many as 80 people capsized and sank in Indonesia's giant Lake Toba, a popular tourist area, on Monday amid bad weather, with one person confirmed dead and only 19 being found alive, government officials said.

National Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said the KM Sinar Bangun was on its way from Samosir, a volcanic island in the middle of the country's largest lake, to the town of Parapat, a few kilometers away, when it sank at 5:30 p.m.

Maher Tamba, chief of the local disaster mitigation agency, said the survivors were rescued by other boats.

The lake, located in the northern part of Sumatra Island about a three-hour drive from the island's largest city of Medan, is the largest volcanic lake in the world.

It is a popular spot for local and international tourists.

But it was not immediately clear whether any foreigners were among the passengers, most of whom were believed to be holidaymakers enjoying the country's 12-day-long Eid al-Fitr holiday.