Rescue efforts were still going on in Indonesia after a volcano-triggered tsunami killed more than 400 people on Saturday, with authorities warning residents to stay away from beaches and the coastline as seismic activity was continuing.

Indonesia’s national disaster agency said the casualty figures would rise. More than 1,000 were injured when the tsunami struck on Saturday evening, the agency added.

“1,459 people are injured, while 128 remain missing,” said agency spokesman Sutopo Purwo Nugroho in a statement.

“The likelihood of further tsunamis in the Sunda Strait will remain high while Anak Krakatoa volcano is going through its current active phase because that might trigger further submarine landslides,” Richard Teeuw of the University of Portsmouth in England told AFP.

Saturday’s rare volcano-sparked tsunami is thought to have been caused by an underwater collapse of part of the volcano. Anak Krakatoa, which forms a small island in the Sunda Strait between Java and Sumatra, emerged in about 1928 in the crater left by Krakatoa, whose massive eruption in 1883 killed at least 36,000 people and affected global weather patterns for years.

Rescuers used diggers and other heavy equipment to remove debris from the affected areas around the Sunda Strait on Monday, while thousands were evacuated from the region.

“The military and police are searching the ruins to see if we can find more victims,” Dody Ruswandi, a senior official at the disaster agency, told AFP, adding that the rescue effort was likely to last at least one week.

Hundreds of buildings were destroyed by the tsunami, which struck the coast of southern Sumatra and the western tip of Java at about 9:30 pm on Saturday after the volcano known as the “child” of Krakatoa erupted.

The tsunami slammed into the shoreline, uprooting trees and leaving debris strewn across beaches. Twisted corrugated steel roofing, timber and rubble were pushed inland at Carita beach, a popular spot for day-trippers on the west coast of Java.

A dramatic video showed a wall of water crashing into a concert by pop group Seventeen, throwing band members off the stage and then swamping the audience. Two band members and the group’s manager were killed, while three others, including the lead singer’s wife, were missing.

Dozens were killed on the Sumatran coast.

Indonesian president Joko Widodo was scheduled to visit the area on Monday. The disaster comes less than three months after a quake-tsunami killed thousands around the city of Palu on Sulawesi island.

Indonesia is one of the most disaster-prone nations on Earth due to its position straddling the so-called Pacific Ring of Fire, where tectonic plates collide.

Unlike most tsunamis which are caused by earthquakes and trigger alarms, this tsunami gave authorities very little time to warn residents of the impending threat.

“It happened very quickly,” said survivor Ade Junaedi. “I was chatting with a guest at our place when my wife opened the door and she suddenly screamed in panic. I thought there was a fire, but when I walked to the door I saw the water coming.”

The International Federation of Red Cross and Red Crescent Societies said the waves reached a height of 30-90 centimeters. Oxfam and other international aid agencies said they would help in the aftermath, as local rescuers evacuated the injured and set up temporary shelters.

“It’s already raining heavily and the winds are strong so we’ve only got a short timeframe to evacuate people and clean up,” said Indonesia’s public works minister Basuki Hadimuljono.

– with reporting by AFP