The Indonesian Meteorology, Climatology, and Geophysical Agency (BMKG) said the wave was not caused by an earthquake, but was possibly the result of volcanic activity at Mount Krakatoa.
Video filmed at one of the affected beaches and posted on Twitter shows the wave rolling in as beachgoers scramble away from the water.
Images from the other side of the Sunda Strait showed the aftermath of the wave.
20 dead as tsunami hits Indonesia beaches – government agency (VIDEO)
Data sementara dampak gelombang pasang di Pantai Anyer Kab Pandeglang dan Lampung Selatan adalah 1 orang meninggal dunia dan 11 orang luka-luka. Korban luka dirawat di rumah sakit. Masyarakat dihimbau tenang. Tidak terpancing pada isu menyesatkan. Tidak ada tsunami. pic.twitter.com/0vJPQtMqip
— Sutopo Purwo Nugroho (@Sutopo_PN) December 22, 2018
Sunda Strait separates the islands of Java and Sumatra. Its coast is located about 100km (62 miles) from the Indonesian capital, Jakarta.
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