Mount Shindake erupted Friday for the second day in a row, the Meteorological Agency said.
The volcano on Kuchinoerabu Island in Kagoshima Prefecture ejected a plume of smoke about 200 meters above the vent at around 9:43 a.m., the agency said.
The island was vacated by its inhabitants due to a larger eruption three weeks ago.
Prior to Friday's activity, an eruption at 12:17 p.m. Thursday lasted about 30 minutes and was followed by another at 4:31 p.m.
The Meteorological Agency warned of the possibility of another eruption similar to the "explosive" May 29 event, which sent black smoke more than 9 km above the crater and caused all 137 islanders to evacuate.