The Indonesian pop-rock band Seventeen was performing over the weekend when an unknown tsunami hit the Sunda Strait, killing band members and fans.

According to lead singer Riefian Fajarsyah, Seventeen’s drummer Windu Andi Darmawan, bassist Muhammad Awal Purbani, and guitarist Hernawan Skiumbang were killed during the storm. Oki Wijaya, the band’s manager, also died, as well as Fajarsyah’s wife, Dylan.

The concert was organized by the state-run electric company PLN. According to CBS 6, the company was unaware of the tsunami until a sudden massive wave erupted, spilling into the stage and across the audience during Seventeen’s performance. The tsunami hit Pandeglang, Serang, and South Lampung, Indonesia, killing at least 373 people. Officials say more than 800 are also injured and many people are missing.

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A concert attendee captured the moment the tsunami crashed into the stage in a video:

Quartz reports that the Indonesian government was unable to warn its citizens of the tsunami since it was not brought on by an earthquake.

“Tsunami warning buoys are positioned to warn of tsunamis originated by earthquakes at underwater tectonic plate boundaries,” professor of planetary geosciences at Open University, David Rothery, told The Guardian. “Even if there had been such a bouy right next to Anak Krakatau, this is so close to the affected shorelines that warning time would have been minimal given the high speeds at which tsunami waves travel.”

The Tsunami may have been caused by the eruption of the Anak Krakatoa volcano, which has been active in recent months. This tragedy follows the 7.5-magnitude earthquake which hit the Indonesian island Sulawesi less than three months ago, killing more than 2,000 people.