Slightly increased volcanic activity has been reported at Mount Io in southwest Japan.

The Meteorological Agency says 2 low-frequency earthquakes occurred at the mountain on Thursday morning.

It said volcanic activity there is picking up slightly, and warned that the mountain may gush out volcanic gas or thermal water within 100 meters of its crater.

The volcano is in the Kirishima mountain range, which straddles the prefectures of Miyazaki and Kagoshima.

The agency maintained its alert level for the mountain at 1 on a scale up to 5.

GPS data suggest that magma has been building up deep underground in the area since last July. But the agency reported no change in ground movement data.

Local authorities are keeping restrictions on entry up to 300 meters from the volcano's crater.