Military helicopters plucked seven people from a Japanese mountainside today after a spectacular volcanic eruption sent officials scrambling to reach many more injured and stranded on the mountain.

Mount Ontake in central Japan erupted shortly before noon yesterday, spewing large white plumes of gas and ash high into the sky and blanketing the surrounding area in ash. About 250 people were initially trapped on the slopes, but most made their way down by yesterday night.

At least 34 climbers have been injured, including 12 seriously, according to Japan's Fire and Disaster Management Agency. The tally was lower than reported by local officials earlier, but the disaster agency warned that the numbers could still change.

The number of those reported missing rose sharply to 32, the agency said.

Japanese television footage showed a soldier descending from a helicopter to an ash-covered slope, helping latch on a man and then the two of them being pulled up. So far, seven people have been picked up in three trips, said Defense Ministry official Toshihiko Muraki. All are conscious and can walk, though details of their conditions are unclear, he said.

The Self-Defense Force, as Japan's military is called, has deployed seven helicopters and 250 troops. Police and fire departments are also taking part in the rescue effort.

An estimated 40 people were stranded at mountain lodges overnight, many injured and unable or unwilling to risk descending 3,067-meter (10,062-foot) Mount Ontake on their own. Rescue workers are also trying to reach the area on foot. A large plume, a mixture of white and gray, continued to rise from the ash-covered summit of the volcano this morning, visible from the nearby village of Otaki.

A convoy of red fire trucks, sirens blaring, and rescue workers on foot headed past barriers into the restricted zone around the mountain.

Shinichi Shimohara, who works at a shrine at the foot of the mountain, said he was on his way up yesterday morning when he heard a loud noise that sounded like strong winds followed by "thunder" as the volcano erupted.

"For a while I heard thunder pounding a number of times," he said. "Soon after, some climbers started descending. They were all covered with ash, completely white. I thought to myself, this must be really serious."

In a video posted on YouTube, shocked climbers can be seen moving quickly away from the peak as an expanding plume of ash emerges above and then engulfs them.