TANJUNG LESUNG, Indonesia — Doctors worked to save injured victims while hundreds of military personnel and volunteers scoured debris-strewn beaches in search of survivors Monday after a deadly tsunami gushed ashore without warning on Indonesian islands, killing more than 280 people on a busy holiday weekend.

The waves that swept terrified locals and tourists into the sea Saturday night along the Sunda Strait followed an eruption and apparent landslide on Anak Krakatau, or “Child of Krakatoa,” one of the world’s most infamous volcanic islands.

At least 281 people were killed and more than 1,000 were injured. Dozens remained missing from the disaster areas along the coastlines of western Java and southern Sumatra islands, and the numbers could increase once authorities hear from all stricken areas.

The Indonesian Medical Association of the worst-affected Banten region said that it sent doctors, medical supplies and equipment, and that many of the injured were in need of orthopedic and neurosurgery surgery. It said most patients are domestic tourists who were visiting beaches during the long weekend ahead of Christmas.

It was the second deadly tsunami to hit seismically active Indonesia this year. A powerful earthquake triggered a tsunami that hit Sulawesi island in September, giving residents a brief warning before the waves struck.

On Saturday night, however, the ground did not shake to alert people before the waves ripped buildings from their foundations and swept terrified concertgoers celebrating on a resort beach into the sea.

Dramatic video posted on social media showed the Indonesian pop band Seventeen performing under a tent on Tanjung Lesung beach at a concert for employees of a state-owned electricity company. Dozens of people sat at tables while others swayed to the music near the stage as strobe lights flashed and theatrical smoke was released. A child could also be seen wandering through the crowd.

Seconds later, with the drummer pounding just as the next song was about to begin, the stage suddenly heaved forward and buckled under the force of the water, tossing the band and its equipment into the audience.

The group released a statement saying their bass player, guitarist and road manager were killed, while two other band members and the wife of one of the performers were missing. On Monday, five more bodies were recovered around the hotel, including a little boy.

“The tide rose to the surface and dragged all the people on site,” the band’s statement said. “Unfortunately, when the current receded, our members were unable to save themselves while some did not find a place to hold on.”

Disaster agency spokesman Sutopo Purwo Nugroho said Monday morning that 281 deaths had been confirmed and at least 1,016 people were injured.

The worst-affected area was the Pandeglang region of Java’s Banten province, which encompasses Ujung Kulon National Park and popular beaches, the agency said.

Indonesian President Joko “Jokowi” Widodo arrived at the disaster area by helicopter on Monday. A day earlier, he 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 Sunday. “Hopefully, those who are left have patience.”

In the city of Bandar Lampung on Sumatra island, hundreds of residents took refuge at the governor’s office, while at the popular resort area of Anyer beach on Java, some survivors wandered in the debris.

Many of the affected areas are popular weekend getaways for residents of Jakarta, Indonesia’s capital, but foreigners were also visiting the area over the long holiday weekend. A Norwegian photographer and volcano enthusiast posted on Facebook that he had to run to escape the waves while on the beach photographing the volcano.

The tsunami was not huge and did not surge far inland, but its force was still powerful and destructive. Hotels and hundreds of homes were heavily damaged by the waves. Broken chunks of concrete and splintered sticks of wood littered hard-hit coastal areas, turning popular beach areas into near ghost towns. Debris from thatch-bamboo shacks was strewn along the coast.

Yellow, orange and black body bags were laid out, and weeping relatives identified the dead.

Scientists, including those from Indonesia’s Meteorology and Geophysics agency, said the tsunami could have been caused by landslides — either above ground or under water — on the steep slope of the erupting volcano. The scientists also cited tidal waves caused by the full moon.

The 305-meter (1,000-foot) -high Anak Krakatau lies on an island in the Sunda Strait between Java and Sumatra islands, linking the Indian Ocean and the Java Sea. It has been erupting since June and did so again about 24 minutes before the tsunami, the geophysics agency said.

The volcanic island formed over years after the 1883 eruption of the Krakatoa volcano, one of the largest, most devastating in recorded history. That disaster killed more than 30,000 people, launched far-reaching tsunamis and created so much ash that day was turned to night in the area and a global temperature drop was recorded.

Most of the island sank into a volcanic crater under the sea, and the area remained calm until the 1920s, when Anak Krakatau began to rise from the site. It continues to grow each year and erupts periodically.

Gegar Prasetya, co-founder of the Tsunami Research Center Indonesia, said Saturday’s tsunami was likely caused by a flank collapse — when a big section of a volcano’s slope gives way. It’s possible for an eruption to trigger a landslide above ground or beneath the ocean, both capable of producing waves, he said.

“Actually, the tsunami was not really big, only 1 metre (3.3 feet),” said Prasetya, who has studied Krakatoa. “The problem is people always tend to build everything close to the shoreline.”

Indonesia, a vast archipelago of more than 17,000 islands and home to 260 million people, lies along the “Ring of Fire,” an arc of volcanoes and fault lines in the Pacific Basin. Roads and infrastructure are poor in many areas, making access difficult in the best of conditions.

A powerful quake on the island of Lombok killed 505 people in August. The tsunami and earthquake that hit Sulawesi in September killed more than 2,100, while thousands more are believed to still be buried in neighbourhoods swallowed by a quake phenomenon known as liquefaction.

Saturday’s tsunami also rekindled memories of the massive magnitude 9.1 earthquake that hit Indonesia on Dec. 26, 2004. It spawned a giant tsunami off Sumatra island, killing more than 230,000 people in a dozen countries — the majority in Indonesia.

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Associated Press writers Margie Mason and Ali Kotarumalos in Jakarta, Indonesia, contributed to this report.

Niniek Karmini, The Associated Press