The wave is thought to have been caused by underwater landslides following an eruption of Mount Anak Krakatau, also known as “Child of Krakatoa”.
Indonesia’s disaster management agency said it was still investigating the incident late on Saturday.
“The impact of the tsunami that hit the coast around the Sunda Strait, especially in Pandenglang District, South Lampung and Serang continues to increase,” said spokesperson Sutopo Purwo Nugroho.
Hundreds of homes have been “heavily damaged” by the disaster.
Thousands of people have been forced to flee their homes and there is no estimate as to the number of people missing.
“The cause of the tsunami is still being investigated. It was possibly caused by underwater landslides due to eruption of Mount Anak Krakatau and tidal waves due to the full moon.
“The two combinations caused a sudden tsunami that hit the coast.”
Dozens of vehicles and buildings including a hotel have been damaged by the tsunami. The affected areas include Tanjung Lesung Beach, Sumur Beach, Teluk Lada Beach, Panimbang Beach, and Carita Beach.
The motorway connecting to the area Serang-Pandeglang, was cut off.
Mr Nugroho said the casualty total was likely to rise but urged the community to “remain calm and not be provoked by misleading issues.”
Mobile phone footage published online shows people trying to flee to safety as the wave rushes through a building.
It comes after nearly 2,000 people were killed by an earthquake and tsunami which struck Sulawesi island on 28 September.
The original Krakatoa volcano was destroyed during a huge eruption in 1883 but the name is still used for the group of islands that remained, including Mount Anak Krakatau.
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