At least 222 people were killed and 800 were injured after a tsunami hit Indonesia’s Sunda Strait on Saturday night.
Some 28 people are still missing following the tragedy, which sent a wall of water some 65ft inland and damaged hundreds of homes.
Scientists from Indonesia’s Meteorology and Geophysics agency said it could have been caused by undersea landslides from the eruption of Anak Krakatau, a volcanic island formed over years from the nearby Krakatau volcano.
They also cited tidal waves caused by the full moon.
Footage posted on social media showed a pop band named Seventeen performing under a tent on a beach as dozens of people sat listening at tables covered in white cloths.
As bright strobe lights flashed on stage, a child could be seen wandering through the crowd, according to the Press Association. Then, in between songs with the drummer pounding, the stage suddenly heaved forward, throwing the band and all their equipment into the audience.
The band released a statement saying their bass player and road manager were found dead, while four other members of their group remained missing.
“The tide rose to the surface and dragged all the people on site,” it said.
“Unfortunately, when the current receded our members are unable to save themselves while some did not find a place to hold on.”
Tourists were also affected during the holiday weekend ahead of Christmas.
“I had to run, as the wave passed the beach and landed 15-20m inland,” Norwegian Oystein Lund Andersen wrote on Facebook.
In the city of Bandar Lampung on southern Sumatra, hundreds of residents took refuge at the governor’s office.
Alif, a resident in Pandeglang district who goes by one name, said the tsunami reached about 9.8ft high. He told MetroTV station that many people were still searching for missing relatives.
Indonesian President Joko “Jokowi” Widodo expressed his sympathy and ordered government agencies to respond quickly to the disaster.
“My deep condolences to the victims in Banten and Lumpung provinces,” he said. “Hopefully, those who are left have patience.”
The Anak Krakatau volcano in the Sunda Strait that links the Indian Ocean and Java Sea erupted about 24 minutes before the tsunami, the geophysics agency said.
The 1,000ft-high volcano, about 124 miles south-west of capital Jakarta, has been erupting since June.
In July, authorities widened its no-go areas to 1.24 miles from the crater.
Gegar Prasetya, co-founder of the Tsunami Research Centre Indonesia, said the waves were likely caused by a flank collapse — when a big section of a volcano’s slope gives way.
He said it was possible for an eruption to trigger a landslide above ground or beneath the ocean, both capable of producing a tsunami.
“Actually, the tsunami was not really big, only one metre,” said Mr Prasetya, who has closely studied Krakatau. “The problem is people always tend to build everything close to the shoreline.”
Physical losses included 430 heavily damaged homes, nine heavily damaged hotels and 10 heavily damaged vessels.
Footage posted by the head of the disaster agency showed the aftermath of flooded streets and an overturned car.
In September, more than 2,500 people were killed by a quake and tsunami that hit the city of Palu on the island of Sulawesi, which is just east of Borneo.