The eruption has killed at least one person and wounded 41 others, officials say of the eruption that covered villages in ashfall and saw people run from billowing clouds of ash and debris.
At least 300 families were evacuated following the eruption, according to Indah Amperawati, deputy head of Lumajang District, an area close to the volcano.
He said that most of the burn victims have been evacuated to the Penanggal Primarily Health Center alongside a resident who died in the village of Curah Kobokan.
Authorities have been unable to reach several other villages due to roads being blocked by mud and fallen trees, Indah told the press conference.
The military has been asked for personnel support and equipment, Maj. Gen. TNI Suharyanto, the head of the National Disaster Management Agency (BNPB), told the press conference.
Budi Santosa, head of disaster management of East Java province, said earlier on Saturday that two sub districts had been “badly affected” by the volcano’s eruption.
Volcanic ash and the smell of sulfur was first reported around 3 p.m. local time (3 a.m ET), the Mount Semeru Volcano Observation Post reported. It added that hot ash clouds were falling towards an East Java village, Sapitarang, in Pronojiwo District.
Videos shared by government emergency response teams showed residents in the area running away from huge thick clouds of ash.
Other footage shared by locals showed people gathering at a local mosque in Besuk Kobokan as ash and smoke blanket the surrounding streets.
Santosa told the news conference that he believed health facilities in the disaster area, either primary health centers or hospitals, would be able to accommodate victims.
His team is trying to conduct evacuations and preparing refugee camps in the area, that would provide food, masks, blankets and shelter for displaced residents.
Indonesia sits between two continental plates on what is known as the Ring of Fire, a band around the basin of the Pacific Ocean that leads to high levels of tectonic and volcanic activity.