The Nuclear Regulation Authority said Monday that the Sakurajima volcano in Kagoshima Prefecture doesn't pose a threat to the Sendai nuclear plant 50 km away.

The Meteorological Agency increased the alert level for the volcano to 4 from 3 on Saturday, advising people within 3 km of the crater to prepare to leave. The highest rating on the scale is 5, when evacuation is ordered because of a high risk of eruption.

Kyushu Electric Power Co., which runs the Sendai nuclear facility, said Monday that operations were normal. A reactor at the facility was restarted last week, the first in Japan to be brought back online under new safety rules set up after the 2011 Fukushima nuclear disaster.