A tsunami apparently caused by undersea landslides from a volcanic island killed at least 20 people after the waves hit the coast around Indonesia's Sunda Strait, the government reported.

Another 165 people were hurt and dozens of buildings damaged Saturday night, the National Disaster Management Agency said.

The Meteorology and Geophysics agency in a separate statement said it could have been caused by undersea landslides from the eruption of Anak Krakatau, a volcanic island formed over years from the nearby Krakatau volcano. It also cited tidal waves caused by the full moon.

The number of victims is likely to increase because not all affected areas have been assessed, said disaster agency spokesman Sutopo Purwo Nugroho.

"I had to run, as the wave passed the beach and landed 15-20m (meters) inland," Øystein Lund Andersen wrote on Facebook. He said he was taking pictures of the volcano when he suddenly saw a big wave come toward him.

"Next wave entered the hotel area where I was staying and downed cars on the road behind it. Managed to evacuate with my family to higher ground trough forest paths and villages, where we are taken care of (by) the locals. Were unharmed, thankfully."

The areas that were affected were South Lampung in Sumatra and the Serang and Pandeglang regions of Java, west of the capital Jakarta. The Sunda Strait between the islands of Java and Sumatra connects the Java Sea to the Indian Ocean.

Footage posted by the head of the disaster agency showed the aftermath of flooded streets and an overturned car.

In September, more than 2,500 people were killed by a quake and tsunami that hit the city of Palu on the island of Sulawesi, which is just east of Borneo.