JAKARTA, Indonesia — Indonesia raised its alert level, widened an exclusion zone, and rerouted flights on 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 6 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 is 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 to 3, or ‘‘caution,’’ on Thursday, warning people to stay at least 3 miles from the crater and to avoid volcanic dust mixed with the 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 had their paths rerouted on Wednesday and Thursday because of a ‘‘red alert’’ for volcanic ash.
Authorities have also warned people to stay away 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 Indonesia’s National Disaster Management Agency.
In addition to those confirmed dead, 159 people remain missing, with little hope they will be found alive. Nearly 1,500 people were injured and nearly 22,000 have been evacuated from the coast and to higher ground, authorities say.
The rain is also hampering search and rescue efforts, while blocked and clogged roads forced search and rescue teams to use helicopters to assess damage, search for bodies, and evacuate people around the village of Sumur near the southwestern 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 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, Reuters 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 the fatalities were in Indonesia.