Rescuers rushed Sunday to help dozens of hikers stranded on an erupting volcano in central Japan with six people believed to be buried under ash and dozens injured.

Columns of thick white steam were rising from the 3,067-metre (10,121-foot) Mount Ontake, which erupted around noon on Saturday, spewing ash, rocks and steam on otherwise a sunny autumn weekend busy with tourists and hikers.

Seven people were unconscious and buried under ash, national broadcaster NHK said.

One of them was rescued but the others remained on the mountain, NHK said, adding that a total of 42 people were believed to have suffered injuries.

Local media on Saturday reported that a person died, but firefighters said the death had not been confirmed.

A suffocating blanket of ash up to 20 centimetres (eight inches) deep covered a large area of the volcano, trapping climbers and forcing up to 150 to seek refuge in mountaintop shelters at one point.

Local officials believe 45 to 49 hikers sheltered overnight in cabins on the popular mountain, although details remained unclear.

A group of 23 hikers who spent the night in a cabin on Sunday were able to climb down to reach the start of a trail leading to the summit.

A Self Defence Force helicopter rescued a man and a woman near the summit, according to a spokesman at Otaki village, Nagano prefecture.

"The helicopter flew over there very early in the morning to survey the condition. Then it found the two people waving at it," the spokesman told AFP.

"Originally, the rescuers thought it might be difficult to go near them because ashes could rise (and damage the helicopter), but the conditions were better than they believed and they were able to rescue the two people," he said.

The two were able to walk unassisted, but were transported to a hospital for observation, the spokesman added.

Some 230 hikers were able to make it to safe ground on Saturday after the eruption.

Ariel television footage showed a line of rescue workers, wearing orange uniforms or green camouflage, scaling grey, ash-covered trails Sunday.

Among the injured, some were hit by flying rocks or suffered burns after inhaling hot volcanic ash, the Yomiuri Shimbun said.

The meteorological agency forecast further eruptions, warning that volcanic debris may settle within four kilometres (2.5 miles) of the peak.

The agency also placed restrictions on access to the mountain, while calling on local residents to remain alert as an eruption could shatter windows miles away.

The last significant eruption of Mount Ontake, which straddles Nagano and Gifu prefectures in the centre of the country, was in 1979 when it expelled more than 200,000 tonnes of ash, according to local media.

A more moderate eruption was last seen in March 2007.

One dead, dozens stranded on erupting Japanese volcano
Tokyo (AFP) Sept 27, 2014 - Dozens of hikers were stranded Saturday on the slopes of an erupting Japanese volcano that has reportedly killed one person and left 30 more seriously injured.

Ash, rocks and steam continued to spew from Mount Ontake more than nine hours after it sprang violently to life as around 250 people were trying to scale its peak.

Four people were buried by the ash, with one having been dug out, Kyodo News reported.

"I first thought it was thunder as I heard a bang and another bang, two or three times," a trekker told public broadcaster NHK. "Then volcanic dust fell noisily."

Amateur cameraman Keiji Aoki told Jiji Press: "It was tremendous. I prepared for death when I got caught in the dust under a pine tree."

A suffocating blanket of ash up to 20 centimetres (8 inches) deep covered a large area of the 3,067 metre (10,121-foot) volcano, trapping climbers and forcing up to 150 into mountaintop shelters at one point.

Around 230 people have now reached the bottom but a further 40 are trapped at the summit where they will spend the night in shelters, local media reported.

Aerial footage of Mt. Ontake showed several cabins smothered with the thick dust, some with windows that appear to have been shattered by the force of the eruption.

NHK said 32 people had been seriously injured, including more than 10 who were unconscious. The broadcaster said one woman was now known to have died.

- Troops sent to rescue hikers -

The eruption came on a busy autumn day on a mountain popular among hikers at this time of year.

Footage apparently filmed by someone on the volcano as it erupted showed towering columns of thick smoke surging into the air and then cascading down its flanks, enveloping walkers.

"The speed of the smoke was too fast. You can't escape," a climber told NHK. "I'm worried that many more people are still on the mountain."

Another climber told how it became impossible to breathe and said rocks were falling "like hailstones".

In Tokyo, Prime Minister Shinzo Abe ordered the military to send troops to the peak to rescue hikers.

"We have confirmed that there have been injuries," Abe told reporters. "I ordered (government officials) to do their best to secure the safety of mountain climbers."

Earlier in the day, local authorities said they had received reports from people on the mountain that at least 11 hikers had been injured, including seven unconscious.

"We are trying to confirm the reports," said Sohei Hanamura, an official of the Nagano prefectural government.

"We have not received any reports of death but we are afraid that the number of casualties would increase," Hanamura told AFP by phone.

NHK said three people were trapped outside by the ash and rocks falling around them.

"There was a thunder-like noise and the sky became dark because of the smoke," Shuichi Mukai, who runs a mountain lodge near the summit, told Kyodo News.

Climbers who fled the eruption spoke of their relief.

"I escaped with my life," a local resident told NHK. "Immediately after I saw the eruption, I rushed away but I was soon covered with ash."

Another male climber told how he had cowered behind a rock during the worst of the eruption.

"No one could escape while the smoke was so intense," he said.

The meteorological agency forecast further eruptions, warning that volcanic debris may settle within four kilometres (2.5 miles) of the peak.

The agency also placed restrictions on access to the mountain, while calling on local residents to remain on alert as an eruption could shatter windows miles away.

The last significant eruption of Mount Ontake, which straddles Nagano and Gifu prefectures in the centre of the country, was in 1979 when it expelled more than 200,000 tonnes of ash, according to local media.