Mount Aso in Kumamoto Prefecture erupted early Saturday, belching a column of ash 11,000 meters into the air.
The explosive eruption occurred around 1:46 a.m. on one of the peaks of the 1,592-meter-high mountain, the Meteorological Agency said. There were no immediate reports of injuries.
It was the first explosive eruption at that particular peak since January 1980.
The agency raised the alert level for the volcano to level 3 on a scale of 5 and urged people not to approach the mountain.
Footage on NHK public television showed orange flames billowing from several locations on the mountaintop as the volcano emitted thick gray smoke into the sky.
Prime Minister Shinzo Abe told reporters Saturday that the government will respond to the disaster.
“We will proceed cautiously and do our best to make lives a top priority,” he said.
The eruption did cause train delays in some areas. Kyushu Railway Co. suspended services on a 38-km-long section between Aso and Bungo Taketa stations on the Hohi Line, which runs on the northern flanks of the volcano.
Air travel was largely unaffected, with the exception of some delayed flights.
Also, around 29,000 residences in the city of Aso and three other nearby municipalities suffered a brief power outage.
There are no houses within the off-limit area and no major damage has been reported in nearby towns.
Volcanic ash accumulated on cars, houses and roads in the city of Aso.
The weather agency warned that ash could even travel as far as Hyogo Prefecture. Falling ash has been observed as far away as the city of Takamatsu, Kagawa Prefecture, on the island of Shikoku, more than 300 km (just under 200 miles) away from the eruption point.
Farmers and producers of fruits and vegetables, such as strawberries and spinach, in Kumamoto Prefecture expressed concern over the ash as they prepare to harvest their crops.
A window at a youth center just a few kilometers away from the mountain suffered a crack, apparently from volcanic rocks.
Masaaki Yamamoto, a manager at the center, told NHK that he heard small volcanic rocks hitting the exterior of the building, and found a crack in the window along with nearby chunks of volcanic debris about the size of a golf ball.
There was also a small-scale eruption at 9:52 p.m. Friday, the agency said. Apart from that, the most recent eruption occurred on May 1.
“Mount Aso is in an unstable condition and could erupt again on the same scale,” an agency official told reporters, warning residents of volcanic ash, rocks and gas.
It is unclear whether the eruption was related to powerful earthquakes that hit Kumamoto and neighboring Oita Prefecture in April, killing 49 people, the official said.
The government of the city of Aso opened shelters at 10 locations and the central government set up a liaison center in the Prime Minister’s Office.
On Mount Aso, three tourists were killed by large rocks thrown up in an eruption in September 1979.
An eruption with pyroclastic flows was also observed in September 2015.
Japan, with scores of active volcanoes, sits on the so-called Pacific Ring of Fire, where a large proportion of the world’s quakes and volcanic eruptions are recorded.
On Sept. 27, 2014, Japan suffered its deadliest eruption in almost 90 years when Mount Ontake, in Nagano Prefecture, unexpectedly burst to life.
An estimated 63 people were killed in the shock eruption that occurred as the peak was packed with hikers out to see the region’s spectacular autumn colors.
The country has around a dozen volcanic warnings in effect at present.