Indonesia's disaster mitigation agency, BNPB, warned residents not to conduct any activities within 5 km (3 miles) of the eruption centre and to stay 500 metres (1,500 feet) from riversides due to risks of lava flow.

Teriring doa untuk semua saudaraku yang berada di kawasan sekitar Gunung Semeru yang saat ini tengah erupsi.

Semoga semua senantiasa berada dalam lindungan-Nya. Stay safe 🙏 pic.twitter.com/bG5aIa83s9

— The Reds Indonesia (@The_RedsIndo) December 4, 2022

Japan's Meteorology Agency said was monitoring for the possibility of a tsunami there after the eruption, public broadcaster NHK reported.

The volcano began erupting at 2:46 a.m. (1946 GMT on Saturday), BNPB said in a statement. Videos posted on social media showed grey ash clouds in nearby areas.

BNPB did not immediately respond to Japan's warning of tsunami risk.

Indonesian authorities have distributed masks to local residents, BNPB said in a statement, adding that volcanic activity remained at level III, below the highest level of IV.

The highest mountain in Java erupted in December last year, ejecting volcanic ash into the sky and raining hot mud on villages as thousands of panicked people fled their homes.

51 people were killed in the December eruption.

In the wake of the eruption, the Center for Volcanology and Geological Hazard Mitigation (PVMBG) warned nearby residents not to conduct any activities within a five km (three miles) radius of the eruption centre and to keep a 500 metre (1,500 feet) distance from riversides due to risks of lava flow.

PVMBG also told people to not conduct any activities within 13 km (eight miles) southeast of the eruption centre.

With 142 volcanoes, Indonesia has the largest population globally living in close range to a volcano, including 8.6 million within 10km (six miles).