Semeru in the eastern part of the Indonesian island of Java is one of the country's approximately 130 active volcanoes.
On Saturday, an extensive eruption was reported with large amounts of smoke and ash.
Pictures show how residents in the region, including the Lumajang district, abandoned their homes and fled the ash cloud that spread in the area.
As a result, the bridge connecting Lumajang and the nearby city of Malang was closed.
"There has been an extremely high pressure since the outbreak," Thoriqul Haq, district leader in Lumajang, told Reuters.
No deaths, injuries or damage to buildings have been reported so far, the country's disaster authority said, adding that evacuation tents have been set up to help those in need.