TOKYO, Jan. 23 (Xinhua) -- Mount Kusatsu-Shirane in Gunma Prefecture, northwest of Tokyo, erupted on Tuesday morning, the weather agency said, triggering a nearby avalanche.

Around 15 people were injured as a result of the eruption, local firefighters said, with four people caught up in the neighboring avalanche at Kusatsu International Ski Resort in Kusatsu-machi, also in Gunma prefecture.

According to the Japan Meteorological Agency (JMA), smoke was initially seen rising from the south side of the volcano and a volcanic tremor with a large amplitude was also observed.

Rocks were seen falling from the site of the volcano, the JMA and local reports also said.

As result of the eruption, the JMA raised its warning for Mt. Kusatsu-Shirane to level 3 on its scale which peaks at 5, instructing people not to approach the volcano.

Mt. Kusatsu-Shirane is a 2,160-meter active volcano with its summit located north of the Asama volcano.

It consists of a series of overlapping pyroclastic cones and three crater lakes.

The largest crater is Yu-gama, an acidic lake with a blueish hue. The surface of the lake has yellow sulfur floating on its surface.

The series of volcanic peaks are located just outside the town of Kusatsu Onsen, which is popular for walkers and hikers as well as those looking to enjoy natural hot springs.