A Japanese scientist has warned Mount Fuji is due for a "big-scale explosive eruption" that could affect millions of people and cause billions of dollars worth of damage.

Last month a study found the magma chamber under the mountain has come under immense pressure, which could even trigger a volcanic eruption.

It said the added pressure could have been caused by last year's earthquake, which was followed a few days later by another large tremor directly underneath Fuji.

Professor Toshitsugu Fujii, the head of Japan's volcanic eruption prediction panel, says an eruption could cause chaos and carnage all the way to Tokyo.

"Mount Fuji has been resting for 300 years now, and this is abnormal," he told Saturday AM.

"It usually erupts in some form every 30 years.

"So the next eruption could be a big-scale explosive eruption."

Ever since last year's massive 9.0-magnitude earthquake off Japan's north-east, the country's meteorological agency has been keeping a closer eye on Mount Fuji.

Of even greater concern to the agency was a magnitude-6.2 quake right under the volcano a few days after the big one.

"It's known that when a large earthquake happens, it can trigger a nearby volcano to erupt," Professor Fujii said.

"That's what happened 300 years ago, when Fuji erupted just 40 days after a big quake."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 3 minutes 28 seconds 3 m 28 s Scientists fear Mount Fuji eruption ( Mark Willacy ) Download 1.6 MB

If there is a large eruption, the government fears it could cause more than $30 billion in damage to public health and agriculture.

Ash accumulations in some areas could be as high as 60 centimetres.

Even Tokyo, 100 kilometres to the north-east, could be coated in volcanic ash.

"Volcanic rocks will fall near the mountain," Professor Fujii said.

"Tokyo will be covered in a few centimetres of ash. Yokohama will be under 10 centimetres.

"Trains will stop, planes won't fly and crops will fail.

"Millions will be affected."

For the hundreds of thousands who live in the shadow of Fuji, an eruption is a constant worry.

Haruo Tomitsuka, a professional photographer who lives by a lake on the east side of the mountain, has been taking photos of Fuji for nearly three decades.

"I'm worried about an eruption, but mostly I worry it will change the beautiful shape of the mountain," he said.

But for now Fuji remains a sleeping giant, and everyone living in the shadow of the national symbol is hoping the volcano's slumber will long continue.