Indonesia's Mount Ili Lewotolok erupted on Sunday, belching a column of smoke and ash four kilometres into the sky, triggering a flight warning and the closure of the local airport.
There were no reports of injuries or damage from the eruption in a remote part of the Southeast Asian archipelago.
But authorities raised the volcano's alert status to its second-highest level as they warned of possible lava flows.
A two-kilometre no-go zone around the crater was also expanded to four kilometres, while flights were advised to steer clear of the area as volcanic ash rained down on East Nusa Tenggara's Wunopitu airport, which was temporarily closed.
"People are advised to not carry out any activities within a four-kilometre radius from the crater," Indonesia's geological agency said.
Indonesia is home to about 130 active volcanoes due to its position on the "Ring of Fire", a belt of tectonic plate boundaries circling the Pacific Ocean where frequent seismic activity occurs.
In late 2018, a volcano in the strait between Java and Sumatra islands erupted, causing an underwater landslide that unleashed a tsunami which killed more than 400 people.