One person has died and dozens are injured after a volcano erupted on Indonesia's Java island, officials said on Saturday.

Residents were filmed fleeing a giant ash cloud from Mt Semeru.

Witnesses described nearby villages covered in debris, and thick smoke blotting out the Sun, leaving them in pitch darkness.

The deputy chief of Lumajang district put the number of injured at 41, saying they had suffered burns.

Indah Masdar called for helicopters to help rescue at least 10 people trapped in buildings.

"We're in big distress," says Masdar. "It's harrowing, their families are all crying."

Indonesia's disaster mitigation agency BNPB later said it knew of 35 people being treated at local medical facilities.

Evacuation efforts have been hampered by choking smoke, a power blackout, and rainstorms during the eruption which turned the debris into mud.

Thoriqul Haq, a local official, told Reuters that a road and bridge from the area to the nearby city of Malang had been severed.

"This has been a very pressing, rapid condition since it erupted," says Haq.

Several hundred people have been moved to shelters or left for safer areas, local broadcaster tvOne quoted him as saying.

The eruption took place at about 2.30pm local time. Local authorities have set up a restricted zone within 5km of the crater.

Airlines have been warned of an ash cloud rising up to 15,000m.

The Volcanic Ash Advisory Centre (VAAC) in Darwin, Australia says the ash appeared to have detached from the summit and was drifting south-west over the Indian Ocean.

The VAAC provides advice to the aviation industry about the location and movement of potentially hazardous volcanic ash.

Campbell Biggs, a meteorologist at the VAAC, told the BBC that the 15,000m plume was higher than the cruising altitude for most aircraft and would cause most flights in the vicinity to divert their flight paths to avoid it.

Ash that solidifies on cooler parts of plane engines can disrupt airflow, which can lead to engines stalling or failing completely.

It also affects visibility for the pilots and can affect air quality in the cabin - making oxygen masks a necessity.

Mt Semeru was quite an active volcano that regularly spewed ash up to about 4300m, so Saturday's eruption was a "pretty significant increase in intensity,” says Biggs.

The ash cloud should slowly dissipate, he says.

Mt Semeru rises 3676m above sea level and previously erupted last December, forcing thousands of residents to seek shelter.

It is among Indonesia's nearly 130 active volcanoes.

Indonesia is on the Pacific "Ring of Fire" where continental plates meet, causing frequent volcanic and seismic activity.

Videos shared by emergency officials and local media showed residents running away as a giant ash cloud rose behind them.

16.50
BPBD Provinsi Jatim dan BPBD Lumajang telah menuju lokasi untuk melakukan assesment dan evakuasi warga di sekitar Gunung Semeru. Silahkan mention jika ada yang dilokasi@PRB_BNPB pic.twitter.com/DYj8qIW23u

— jogjaupdate.com (@JogjaUpdate) December 4, 2021

Kondisi erupsi Semeru saat ini. Silahkan mention jika ada yg dilokasi pic.twitter.com/5nnvqyoVJg

— PRB Indonesia BNPB (Disaster Risk Reduction) (@PRB_BNPB) December 4, 2021

Info saat ini bahwa jembatan Gladak perak putus. Tolong menginfokan kepada masyarakat yang akan melewati lokasi ini untuk berhati-hati pic.twitter.com/Cgap7SZwBz

— PRB Indonesia BNPB (Disaster Risk Reduction) (@PRB_BNPB) December 4, 2021

RNZ