Authorities urged tourists and others to stay at least 6km from the 725m Ruang volcano.
Officials worry that part of the volcano could collapse into the sea and cause a tsunami as happened in an 1871 eruption there.
Tagulandang island, to the volcano’s northeast, is again at risk, and its residents are among those being told to evacuate.
Indonesia’s National Disaster Mitigation Agency said residents will be relocated to Manado, the nearest city, on Sulawesi island, a journey of six hours by boat.
In 2018, the eruption of Indonesia’s Anak Krakatau volcano caused a tsunami along the coasts of Sumatra and Java after parts of the mountain fell into the ocean, killing 430 people.