Japan's Mount Fuji may be sitting on a large, active fault that could trigger a magnitude-7 earthquake, changing the shape of the mountain and devastating nearby communities, the education ministry said.

A survey commissioned by the ministry found a 30-km fault beneath Japan's highest mountain, believed by many to be sacred, and research results indicate it was likely to be active, a ministry official said on Thursday.

If the fault sets off an earthquake, it could lead to a major landslide and hit communities at the foot of the 3,776-metre-high mountain. Further research was required, the official said.

A magnitude-9 earthquake and massive tsunami hit northern Japan last year, leaving nearly 19,000 people dead or missing and causing the world's worst nuclear disaster in 25 years.

An earthquake in 1707 caused Fuji to erupt and killed an estimated 20,000 people. - Reuters