Sutopo Purwo Nugroho, head of public relations at Indonesia's National Disaster Mitigation Agency, said earlier two people are missing.

"We are still gathering information," Nugroho said. "The worst hit area is Pandeglang district, along the coastal area, including residential and tourist areas in the Tanjung Lesung beach, Lesung beach, Teluk Lada, Panimbang and Carita beach."

The tsunami was likely caused by a combination of underwater landslides due to a volcanic eruption, the country's meteorological, climatological and geological agency said.

"The Geological Agency detected at 21.03 local time the Anak Krakatau erupted," Indonesia's Meteorology, Climatology, and Geophysical Agency said, adding that the tsunami struck 24 minutes later. "It's possible the materials around Anak Krakatau collapsed to the sea and triggered the tsunami and affected beaches around Sunda Strait."

Some residents fled to shelters after the tsunami hit.

Kathy Mueller, a spokesperson for the International Federation of Red Cross and Red Crescent Societies in Indonesia, told CNN that the organization expects the death toll to rise.

"It's so early after the disaster, the numbers will fluctuate and it will take a while before the picture becomes clearer... It's a very fluid situation and the numbers are going to change," Mueller said by phone.

She added that because of the holiday season, "the area of Pandeglang would have been crowded with local tourists when the waves came in."

Red Cross teams are bringing in basic household items, clean water and equipment to help clear away debris, Mueller said.

But the organization has been told that the main road between the two affected areas is damaged, she said, so accessing them may be challenging.

Indonesia has been hit by a series of natural disasters in recent weeks, including a powerful earthquake that hit the island of Sulawesi on September 28. In the towns of Baleroa and Petobo, rivers of soil swept away entire neighborhoods in the aftermath of the magnitude-7.5 earthquake and ensuing tsunami.

The death toll from the quake is nearly 2,000.

In October, torrential rains and flooding triggered mudslides that wiped out part of an elementary school in Indonesia's North Sumatra. Twenty people were killed.

CNN