Indonesia's Mount Semeru erupted Sunday, spewing hot ash clouds a mile into the sky, prompting authorities to raise the volcano's alert status to the highest level.
The eruption of the highest mountain on Indonesia's main island of Java around 800 kilometers southeast of the capital of Jakarta sparked evacuations of nearby villages.
The increased threat level "means the danger has threatened the people's settlement and the volcano's activity has escalated," Volcanology and Geological Disaster Mitigation Center (PVMBG) spokesperson Hendra Gunawan told broadcaster Kompas TV.
"Japan's weather agency warned that a tsunami could arrive at the islands of Miyako and Yaeyama in the southern prefecture of Okinawa," Kyodo news agency reported.
It said the tsunami could arrive by 2:30 pm local time (0530 GMT) but there were no reports of any damage an hour after that time had passed.
"Hot avalanches" caused by piles of lava at the tip of the volcano slid down after the eruption, National Disaster Mitigation Agency spokesperson Abdul Muhari said.
No casualties or injuries were immediately reported after the eruption, but Gunawan warned nearby residents not to travel within eight kilometers of the crater after the threat level was raised to four.
Shelters were being prepared for residents who were evacuating, the official said.
They were also told to avoid a southeastern area 13 kilometers along a river in the direction where the ash was travelling.
"A lot of people have started to go down," Thoriqul Haq, the local administration chief for Lumajang, where the volcano is located, told broadcaster Kompas TV.
Video footage circulating on social media showed plumes of hot smoke rising from Semeru and at least one village covered in ash and the air a dark haze.
One year after last eruption
The internet was cut and phone signals were patchy after the eruption, according to an AFP journalist.
The local rescue agency distributed free masks to the public because of the threat of polluted air to vulnerable residents.
Mount Semeru last erupted exactly one year ago, killing at least 51 people.
The disaster left entire streets filled with mud and ash, swallowing homes and vehicles, with nearly 10,000 people seeking refuge.
Semeru's alert status had remained at its second-highest level since its previous major eruption in December 2020, which also forced thousands to flee and left villages covered.
Indonesia sits on the Pacific Ring of Fire, where the meeting of continental plates causes high volcanic and seismic activity.
The Southeast Asian archipelago nation has nearly 130 active volcanoes.
In late 2018, a volcano in the strait between Java and Sumatra islands erupted, causing an underwater landslide and tsunami which killed more than 400 people.