JAKARTA, Indonesia (AFP) — 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 capital 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 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 p.m. local time but there were no reports of any damage an hour after that time had passed.

"Hot avalanches" caused by piles of lave 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 traveling.

"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.