The unexpected eruption of a volcano in a popular upland tourist district sent authorities scrambling to get word to tourists and residents on Thursday.

Mount Asama spewed smoke and ash for about 20 minutes the previous evening. It last erupted in 2015, and was on the Meteorological Agency's lowest alert level.

One of Japan's most active volcanos, the cone-shaped mountain towers over popular summer retreats such as Karuizawa in Nagano and the village of Tsumagoi in Gunma. The eruption at 10:08 p.m. Wednesday at a location near the crater sent smoke to an altitude of about 1,800 meters, according to the agency. The 2,568-meter-high volcano sits on the border of Nagano and Gunma prefectures.