UPDATE (AP): A volcano erupted in central Japan on Saturday, catching mountain climbers by surprise and trapping more than 250 people. At least 11 people were injured, including seven who were unconscious.

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.

Eleven people were injured, eight seriously, including the seven who lost consciousness, Kashiwabara said.

On the Gifu prefecture side of the mountain, 52 people were able to descend, the Fire and Disaster Management Agency said.

Mikio Oguro, an NHK journalist who was on the slope on an unrelated assignment, told the station that he saw massive smoke coming out of the crater, blocking sunlight and reducing visibility to zero.

"Massive ash suddenly fell and the entire area was totally covered with ash," he said by phone. He and his crew had to use headlights to find a lodge to take refuge.

"My colleagues later told me that they thought they might die," Oguro said.

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TOKYO (TheBlaze/AP) — A volcano erupted in central Japan on Saturday, sending a large plume of ash high into the sky, prompting a warning to climbers and others to avoid the area and bringing one question to the minds of a watching world: Is everyone ok?

Mt Ontake eruption. Sep 27 around noon, JST. pic.twitter.com/GfW95WxGIp

— 　　　　Shisui/شيسوي（紫水） (@4su1) September 27, 2014

Japanese broadcaster NHK, citing local authorities, said there were reports of injuries, but no word on their severity. It also reported that people had been evacuated from a mountain lodge.

But at least one person appears to have gone completely off the map.

Twitter user setori_ tweeted a photo from the mountain just prior to the eruption, and as of Saturday evening in Japan (seven hours after the eruption), the account had not tweeted again.

Hiker on Mt. Ontake tweeted this photo of the volcano crater one minute before the eruption, and hasn’t tweeted since pic.twitter.com/B5S2O6SH9q

— Jon Passantino (@passantino) September 27, 2014

Mt. Ontake erupted shortly before noon on a bright sunny morning. The 3,067-meter (10,062-foot) peak sits on the border of Nagano and Gifu prefectures on the spine of mountains that runs down Honshu, Japan's main island.

9合目避難小屋から9合目石室山荘小屋まで退避 雲と空と岩の世界が火山灰の死の大地に… #噴火 #御嶽山 pic.twitter.com/DRa2onaXZO

— あべるん (@avel_yasuda) September 27, 2014

In a YouTube video shown on NHK, climbers can be seen moving quickly away from the peak as an expanding plume emerges above them.

Japan's meteorological agency raised the alert level for Mt. Ontake to three on a scale of one to five. It warned people to stay away from the mountain, saying debris could fall up to 4 kilometers (2.5 miles) away.

MAP (@flightradar24): Mt. Ontake, located about 100km NE of Nagoya, erupted on Saturday. Most flights take a detour pic.twitter.com/keEkvMBXX5

— TheBlazeNOW (@TheBlazeNOW) September 27, 2014

This story has been updated

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