TOKYO (AP) — Mount Aso in southern Japan sent huge plumes of gray smoke as high as 11 kilometers (6.8 miles) into the air on Saturday in one of the volcano's biggest explosions in years.

The Japan Meteorological Agency said the explosion in the early hours of Saturday also blew off bits of volcanic rock and ash and raised the alert level for the area, extending the entry ban from just around the volcanic mouth to the mountain itself.

Footage on Japan's NHK public television showed orange flames flickering from several locations on the mountaintop as the volcano emitted thick gray smoke billowing into the sky.

There are no homes within the off-limit area and no injuries or major damage have been reported in nearby towns, though buildings and cars were covered with thick ash falls. Flights were largely unaffected, except for some delays.

A window at a youth center just a few kilometers (miles) 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 chunks of volcanic debris about the size of a golf ball near it.

Aso city, about 10 kilometers (6 miles) north of the volcano, set up evacuation centers as a precaution. Residents were washing off ash from external walls, plants and the streets before it dries up and spreads farther. Media reports said some ash falls were detected in parts of western Japan.

The area is still recovering from deadly earthquakes in April.

Mount Aso has repeated smaller eruptions in recent years. The agency said it was not known if the volano's recent activity was related to the earthquakes earlier this year, but it's in an unstable condition and could erupt again.

Japan sits atop the Pacific "ring of fire" and has more than 100 volcanoes.

Mount Aso had a smaller eruption in August while eruptions in 2014 disrupted tourism in the area.

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