Japan's weather agency said Wednesday it is assessing the tsunami risk to the country following a large-scale volcanic eruption in Indonesia.

The violent eruption of the Ruang volcano took place at around 9 p.m. Japan time and a large earthquake was detected, the agency said. The focus of the quake was the Talaud Islands in northern Indonesia.

If tsunami waves are generated, they could reach Japan's southern island prefecture of Okinawa around 11 p.m., according to Japan Meteorological Agency.

The size of the potential tsunami is unclear, it added.