With a sound likened to thunder, Mount Ontake erupted shortly before noon, spewing large white plumes of ash high into the sky and sending people on the mountainside fleeing, covering some in ash.

More than 250 people were trapped on the mountain and a nearby peak in areas that were dangerous to approach, though some had decided to try making their way down as sunset approached, said Nagano prefecture crisis management official Minoru Kashiwabara. MORE