At least 222 people are dead and hundreds more are missing or injured, The Associated Press reports, after a tsunami struck Indonesia late Saturday night local time.
The death toll is expected to rise.
Officials there are blaming the tsunami on underwater landslides caused by volcanic activity on the island of Anak Krakatau, which erupted just after 9 p.m. local time. The tsunami struck around the Sunda Strait, between Java and Sumatra, the two most populous islands in Indonesia.
Footage shared by news outlets and social media show a wave hitting a seaside concert by Indonesian pop rock band Seventeen at a resort on Java, washing away the stage and many people along with it.
Sutopo Purwo Nugroho from Indonesia's disaster management said on Twitter that 556 houses were destroyed.
NPR's Michael Sullivan told host Lulu Garcia-Navarro on Weekend Edition that the tsunami was small, with reports of its height between 3 and 7 feet.
"But on the other hand, it's a very populous island, Java, and Sumatra is also populous in that region, and people tend to build close to the beach," Sullivan said. "So even a small wave, if it's forceful enough, causes the damage we saw in that video."
Red Cross volunteers are helping rescue survivors and recover bodies in Sumatra and Java, according to the International Federation of the Red Cross.
Norwegian photographer ystein L. Andersen was capturing images of Anak Krakatau from the beach when the tsunami hit, he said on Facebook.
"I had to run, as the wave passed the beach and landed 15-20m inland," he wrote. "Managed to evacuate with my family to higher ground trough forest paths and villages, where we are taken care of my the locals. Were unharmed, thankfully."
The 1883 eruption of nearby Krakatoa killed more than 30,000 people. Anak Krakatau, the "son of Krakatoa," emerged from the spot where the island of Rakata had been before that eruption.
Anak Krakatau has seen a series of minor eruptions for several months.
An earthquake and tsunami struck the Sulawesi island city of Palu in September, killing more than 1,700 people.
The 2004 Indian Ocean tsunami, which was triggered by an earthquake, killed about 226,000.
Indonesian authorities have increased the alert level around the Anak Krakatau volcano and rerouted flights after a series of eruptions that triggered a deadly tsunami over the weekend.
An exclusion zone around the volcano, located on an island in the Sunda Strait between Sumatra and Java, was extended to a 3-mile radius.
"All flights are rerouted due to Krakatau volcano ash on red alert," the government air traffic control agency AirNav said in a release quoted by Reuters.
The news agency quoted the country's civil aviation authority as saying no airports would be affected.
On Saturday, a section of the volcano's crater collapsed into the ocean, triggering tsunami waves of more than 6 1/2 feet that crashed into coastlines along the Sunda Strait, killing at least 430 people.
It was the second tsunami to hit Indonesia in the past three months.
Saturday's wave "swept over popular beaches on southern Sumatra and the western edge of Java, inundating tourist hotels and coastal towns, including Sumber Jaya, leaving a trail of death and destruction in its wake," according to Channel News Asia.
As The Associated Press notes, "The disaster struck without warning, taking people by surprise in a country that regularly suffers landslides, earthquakes and volcanic eruptions. No earthquake shook the ground beforehand, and the waves surged inland at night on a holiday weekend while people were enjoying concerts and other beach and resort activities."
Since then, photos taken by Indonesia's National Agency for Disaster Management, or BNPB, show a layer of volcanic ash has settled on buildings and vehicles along the west coast of Java.
The Indonesian government has warned of further tsunami, cautioning nearby communities to stay at least 1 kilometer away from the coastline.
"Since December 23, activity has not stopped ... We anticipate a further escalation," said Antonius Ratdomopurbo, secretary of the geological agency, according to Reuters.
Heavy rains and high seas have hampered search efforts some of the dead have been found at sea. At least 159 are still missing, the AP reports. Nearly 20,000 people have been displaced by the tsunami and nearly 1,500 injured, according to Reuters.
As Reuters notes, "In 1883, [Krakatau] ... erupted in one of the biggest blasts in recorded history, killing more than 36,000 people in a series of tsunami and lowering the global surface temperature by one degree Celsius with its ash. Anak Krakatau is the island that emerged from the area in 1927 and has been growing ever since."