Indonesia has raised the danger level for a volcano that triggered a tsunami over the weekend, which killed at least 430 people in Sumatra and Java, and widened its no-go zone.

The country’s volcanology agency said on Thursday the Anak Krakatau volcano’s alert status had been raised to the second-highest level and the exclusion zone more than doubled to a three-mile radius.

The eruption on Saturday night caused part of the island volcano in the Sunda Strait to collapse into the sea, which in turn is believed to have generated tsunami waves of more than 2 metres (6.5 feet). Most tsunamis are caused by earthquakes.

The government has warned Sunda Strait communities to stay at least a kilometre away from the coastline because of the risk of another tsunami triggered by Krakatau’s ongoing eruptions.

“There’s still a chance of a landslide, even under the sea level or on the sea level,” said Rudy Sunendar, the head of the energy ministry’s geology department. “We don’t know exactly because we are not yet gone to the field” due to bad weather, he said at the volcano’s monitoring post. “Based on the satellite imagery interpretation, there is collapse of some area of Mount Anak Krakatau.”

Saturday’s disaster struck without warning in a country that regularly experiences landslides, earthquakes and volcanic eruptions. No earthquake activity had been felt beforehand, and the waves surged inland at night on a holiday weekend while many people were enjoying concerts and other beach and resort activities.