Ash from the 2,568-meter (8,425-foot) Mount Asama was falling on the northern side of the mountain, the agency said. The eruption was relatively small in scale, and didn’t register strongly on seismometers.
The agency said the volcano is covered by thick clouds, making it difficult to observe any smoke billowing out, but noted there haven’t been any reports of serious explosions involving the spewing of pyroclastic rocks.
It was the volcano’s first eruption since May 2009, a representative for the agency said.
Japan has seen a string of volcanic eruptions in recent months. In May, an “explosive eruption” from Mount Shindake on the small southern island of Kuchinoerabu sent smoke and ash 9,000 meters into the air. The island’s 137 residents were evacuated as a precaution.
In September, Mount Ontake erupted in central Japan, killing more than 50 people.
Japan has 110 active volcanoes, defined as those that have erupted in the past 10,000 years or have shown signs of emitting vapor or gas, according to government data.