More than 1,400 others had sustained injuries, while 128 people were still missing.
Out in the strait, Anak Krakatau, or "Child of Krakatoa", was still erupting and authorities imposed a two-kilometre exclusion zone around it.
Video shot from a charter plane captured the magnitude of the volcanic event in the Sunda Strait, between Sumatra and Java. Officials said heavy rescue equipment and emergency soup kitchens have been deployed. Initially, Indonesia's Meteorology, Climatology and Geophysics Agency (BMKG) thought that the tsunami may have been a mere tidal wave caused by the full moon.
Instead, a volcanic island with an ominous name - Anak Krakatau, or "Child of Krakatoa" - rumbled as it has been doing for months before a giant chunk of it apparently broke loose like a rock falling into a tub, silently unleashing disaster.
"Our sensors can give early-warning signs based on tectonic quakes, because more than 90 percent of the tsunamis in Indonesia are caused by tectonic quakes", Karnawati said.
The Energy and Mineral Resources Ministry's Center for Volcanology and Geological Hazard Mitigation said a tsunami caused by a partial collapse of a volcano was a rare event globally and was hard to predict, but it nevertheless recommended a system of tidal stations, buoys and/or "visual monitoring with remote sensing" in the waters surrounding Anak Krakatau, Bloomberg News reported. Nugroho acknowledged Indonesia's detection buoys have been dysfunctional since 2012, according to the Associated Press, a result of vandalism and budget issues.
Twisted steel girders are all that's left of a music stage after the deadly tsunami.
"Tsunamis from volcanic flank collapse are generated right at the coast and often close to populations", said Eddie Dempsey, lecturer in structural geology at Britain's University of Hull.
Seventeen played to a large crowd attending its concert at the Tanjung Lesung Beach Resort in the Banten Province of Indonesia on Saturday.
"The ideal atmosphere suddenly changed dramatically in just seconds!" recalled Mamad Setiadi, who had helped set up at the Tanjung Lesung Beach Club for the pop band Seventeen, which performed for employees of a state-owned electric company while a comedian simultaneously had audience members laughing in another area of the lawn.
"The tide rose to the surface and dragged all the people on site", it said.
How did the tsunami happen?
Coordinating Maritime Affairs Minister Luhut Pandjaitan said that experts from the BMKG, the Agency for the Assessment and Application of Technology (BPPT) and the Energy and Mineral Resources Ministry would be working on a team to perform marine geological and bathymetric surveys in the area surrounding Anak Krakatau. But its rumblings and eruptions have been described by local experts as relatively low-scale and semi-continuous. And unlike most big waves, typically alerted by an earthquake's violent shaking, this was a stealth attack. "This would have sent millions of tonnes of rocky debris into the sea, pushing out waves in all directions".
Roads and infrastructure are poor in many areas of disaster-prone Indonesia, making access hard in the best of conditions. The Ring of Fire - stretching from New Zealand to Indonesia to Japan on the Asian side, and from southern Alaska down through the Pacific Northwest, California, Mexico and the western coast of South America - is where the continental plates meet, and where most of the world's earthquakes and volcanic activity occur.
When a tsunami hit Indonesia early Sunday - killing more than 350 people and leaving hundreds of others injured or missing - the country's residents were blindsided by the waves.
According to a United Nations report from a regional working group focused on tsunami warning systems, which was held in Vietnam in March, the Indonesia Tsunami Early Warning System (InaTEWS) focuses on quake information and included 170 seismic broadband systems, 238 accelerometer stations and 137 tidal gauges.