Hundreds of people have been evacuated after a large volcano eruption in Indonesia that has also prompted an aviation warning in Australia.

Dramatic video footage of the Mount Semeru eruption shared online shows huge clouds of ash sweeping across a forest into what appears to be a river bed.

The ash column reached up to 2km above the summit of Java’s tallest mountain, according to the country’s volcanology agency.

It increased the alert level of Mount Semeru to the highest, as multiple eruptions sent lava and rocks as far as 13km down the mountain’s slopes.

“Hot clouds are not fog!!” the agency said in a social media post warning people to keep clear of the evacuation zone, adding that the flow of hot ash and lava “can be life-threatening”.

Although there are no reports of casualties, more than 900 residents from nearby have been moved to shelter.

“We’ve also deployed personnel to search for whether there are still residents trapped or not,” said agency official Prahista Dian.

Terjadi erupsi G. Semeru pada hari Rabu, 19 November 2025, pukul 16:00 WIB tinggi kolom abu teramati ± 2.000 m di atas puncak. Erupsi terekam di seismograf dengan amplitudo maksimum 40 mm dan durasi 1000 detik. https://t.co/Z7jNpD8OPx via @id_magma pic.twitter.com/ItYQppcfOG

— Badan Geologi (@badangeologi_) November 19, 2025

The eruption of 3600m-high Semeru – one of Indonesia’s 129 active volcanoes – prompted the Australian Bureau of Meteorology’s Volcanic Ash Advisory Centre to issue a red alert.

Jetstar and Qantas said no flights from Australia to Bali had been impacted but the airlines were monitoring the situation. Passengers were advised to check their flight status online for the latest updates.

Java is the most densely populated island in Indonesia and the eruption has blanketed several villages with falling ash, forcing authorities to raise the volcano’s alert level twice, from the third-highest level to the highest.

Around 170 climbers were stuck overnight at a lakeside camping area at the foot of the volcano about 6.4km from the crater but are safe and now being helped to safety.

Semeru’s last major eruption, in 2021, killed 51 people and injured several hundred more.

Indonesia straddles the “Pacific Ring of Fire,” a highly seismically active zone, where different plates on the earth’s crust meet and create a large number of earthquakes and volcanoes.

–with Reuters / AAP