A "sudden tsunami" has killed at least 20 people in Indonesia.

At least 20 people have been killed by a tsunami that hit beaches in Indonesia after the Krakatoa volcano erupted.

The tsunami hit beaches in the Sunda Strait, which is between the islands of Java and Sumatra, on Saturday night.

At least 165 other people have been injured, Indonesia’s Disaster Mitigation Agency said. Dozens of buildings were damaged.

Pandenglang District, South Lampung and Serang were hardest hit, and the death toll was likely to grow.

The Disaster Mitigation Agency said the tsunami was possibly caused by landslides due to the eruption of Krakatoa and tidal waves due to the full moon.

“The two combinations caused a sudden tsunami that hit the coast,” the agency said.

MORE: the #Tsunami in #Indonesia happened not long after a #volcano in the area. pic.twitter.com/jvqe4RFGdr

— David Shapira (@David_shapira) December 23, 2018

#Tsunami wave or something like it in Anyer. Panik here pic.twitter.com/p8lhEfcfC7

— Øystein L. Andersen (@OysteinLAnderse) December 22, 2018

BREAKING: At least 20 dead after a tsunami, likely caused by the eruption of Krakatau has stuck parts of Indonesia
pic.twitter.com/Z81HenAaoE

— Global News Network (@GlobalNews77) December 22, 2018

Volcano photographer Oystein Andersen posted on Twitter that he was on the beach observing the Krakatoa after explosions earlier in the evening when the waves came.

“I was at the beach and saw the waves,” he wrote. “I ran.”

Videos posted on social media show flooded streets, an overturned car and people running up stairs to escape the waves.

The 1883 eruption of Krakatoa was one of the deadliest volcanic eruptions in the world, killing more than 36,000 people.