Mount Aso, a volcano on Japan's main southern island of Kyushu, explodes early on Saturday, Japan's Meteorological Agency said, spewing volcanic ash 11,000 meters (7 miles) into the sky.
Police and municipal governments said there were no reports of injuries from the eruption, which began at 1:46 a.m. local time (1646 GMT Friday) on one of the peaks of the 1,592-metre (5,222 feet) mountain in Kumamoto Prefecture.
It was the first "explosive eruption" at the peak since January 1980, according to the meteorological agency. The agency raised the alert level for the volcano to level 3 on a scale of 5, telling people not to approach the mountain and warning of falling rocks. It also warned of falling ash in 10 prefectures.
TV footage showed volcanic ash had accumulated on cars, houses and roads in the city of Aso and ash was falling as far as 320 km (200 miles) away, Japanese media said. Farmers have reported that some vinyl greenhouses where tomatoes and asparagus were being grown 6-8 km (4-5 miles) away from the crater had been broken by ash and small rocks.
A window was cracked by a falling rock at an Aso youth center about 5 km (3 miles) away from the crater but there were no reports of injuries, an official at Aso city hall said. "We are concerned that more damage on crops will be reported," the official said.
Kyushu Electric Power Co said the eruption had no impact on its Sendai nuclear plant, which is about 160 km (100 miles) south of Mount Aso and is one of the two reactors that are online in Japan.
Up to 29,000 households lost power shortly after the eruption but the problem was fixed in less than two hours, a spokesman at Kyushu Electric said. Mount Aso is one of the most active peaks in Japan but is also a popular hiking spot.
Japan lies on the "Ring of Fire", a horseshoe-shaped band of fault lines and volcanoes around the edges of the Pacific Ocean, and is home to more than 100 active volcanoes.
Mount Ontake in central Japan erupted unexpectedly in 2014, killing 63 people in the worst volcanic disaster in Japan for nearly 90 years. Mount Aso also erupted in September last year, blasting a plume of black smoke 2 km (1.2 miles) high.