JAKARTA, Indonesia — Indonesia raised its alert level, widened an exclusion zone and rerouted flights Thursday as eruptions again intensified from an island volcano that triggered a deadly tsunami at the weekend.

A landslide that followed a large eruption of Anak Krakatau on Saturday night sent waves between six and 10 feet high crashing into fishing villages and beach resorts on the densely populated islands of Java and Sumatra, killing at least 430 people. 

But the volcano is still erupting and almost obscured by huge clouds of ash and lava billowing into the air. Meanwhile, heavy rain and stormy seas have raised fears that the volcano’s slopes could collapse again, potentially triggering a second tsunami.

The Energy Ministry’s Volcanology and Geological Disaster Mitigation Center raised the alert level Thursday to 3, or “caution,” warning people to stay at least five kilometers (three miles) from the crater and avoid the volcanic dust mixed with falling rain. 

Level 3 is defined as increasing volcanic activity with dangers of an eruption intensifying but not threatening human settlements. The highest alert level is 4.

“When the dust rains down, civilians are advised to put on a mask and glasses when outside the house,” said Antonius Ratdomopurbo, the secretary for the ministry’s geology department.

Indonesia’s air traffic control agency, AirNav, said several flights were rerouted Wednesday and Thursday because of a “red alert” for volcanic ash.

Authorities also have warned people to stay a kilometer from the shore in case another wave hits, and have declared a state of emergency until Jan. 4 to make it easier to deploy assistance to affected areas.

“People are advised to keep calm and stay alert,” said Sutopo Purwo Nugroho, spokesman for the country’s National Disaster Management Agency.

In addition to those confirmed dead, 159 people remain missing. Nearly 1,500 people were injured, and nearly 22,000 have been evacuated from the coast to higher ground, authorities say. 

The rain also is hampering search-and-rescue efforts, while blocked and clogged roads have forced teams to use helicopters to assess damage, search for bodies and evacuate people around the village of Sumur, near the western tip of Java.

“Our main obstacle is with the weather, but the operation is still underway,” said Yusuf Latif, spokesman for Indonesia’s National Search and Rescue Agency. “We got through to areas that were previously deemed isolated, like the Sumur village and some areas on the west coast of Banten province.”

The surging seawaters have left behind a coastline littered with the debris of crushed homes, wrecked vehicles and fallen trees. They also left dozens of turtles stranded on land, with volunteers helping them back out to sea, the Reuters news agency reported.

The tsunami was the third major natural disaster to hit Indonesia this year, after an earthquake killed more than 500 people on the island of Lombok in August, and an earthquake and tsunami killed more than 2,200 on Sulawesi in September. It also evoked painful memories of the 2004 Indian Ocean tsunami that struck on Dec. 26, 2004, killing more than 220,000 people in a dozen countries. More than half of the fatalities were in Indonesia.

Anak Krakatau, whose name means Child of Krakatoa, rose from the waves in 1927, following the 1883 eruption and collapse of the original Krakatoa volcano. That was one of the largest volcanic eruptions in recorded history, with tsunamis killing at least 36,000 people and clouds of ash depressing temperatures around the globe.