The death toll from the tsunami that slammed into Indonesia rose to 281 Monday while experts are warning that a second deadly wave could be imminent.

Officials say more than 1,000 people were injured and another 57 are missing on the island of Java. The giant wave hit Sunday without warning and damaged more than 600 houses, displacing another 12,000 people.

The country’s tsunami warning system has been inoperable because of vandalism and technical problems since 2012, said Sutopo Purwo Nugroho, head of public relations for the Indonesian National Disaster Mitigation Agency.

Indonesian President Joko Widodo ordered the country to purchase new early warning detectors as soon as possible. He said on Twitter that he’s praying for the victims and will be heading to the disaster zone Monday.

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The tsunami hit beaches full of people, sucking them out to sea without warning. It hit one beach-side concert by the pop group Seventeen, causing the stage to collapse and killed one of the musicians and the group’s manager.

Volcanic activity at Mount Anak Krakatau could trigger additional mudslides that could cause more deadly tsunamis, officials said. The volcano is part of the Ring of Fire, a volcanic hot zone that stretches 25,000 miles from New Zealand to Japan. It’s believed that the eruption forced rock beneath the water to shift, displacing the water above it.

The same Anak Krakatau volcano is blamed for an eruption that killed 36,000 people in 1883.

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A full moon caused a tidal wave that compounded the problems on Sunday.

President Donald Trump reacted to the disaster on Twitter.

“Unthinkable devastation from the tsunami disaster in Indonesia,” Trump said. “We are praying for recovery and healing. America is with you!”

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Pope Francis asked the world to pray for the victims of the disaster.

“My appeal is that these brothers and sisters may not lack our solidarity and the support of the international community,” he said.

Two months ago, a tsunami slammed into the Indonesian island of Sulawesi, killing more than 2,000 people. Indonesia’s worst disaster to date was the 2004 Boxing Day tsunami that killed nearly 230,000.