More than 9,600 people would die with nearly 150,000 injured if a mega-quake struck Tokyo, a disaster that would also level large parts of the Japanese capital, a government projection said Wednesday.

The frightening simulation was released by the Tokyo Metropolitan Government as Japan slowly rebuilds its northeast coast, which was devastated by a magnitude 9.0 quake in March last year that unleashed a deadly tsunami.

The disaster killed some 19,000 people and triggered the worst nuclear accident in a generation.

Tokyo was largely spared from the damage, but if a smaller 7.3-magnitude quake struck the sprawling metropolis it would leave about 9,600 dead and 147,000 people with injuries, including 21,900 seriously, the projection said.

About 5.2 million people would be unable to go home owing to electricity and transportation damage while the temblor would flatten or seriously damage some 378,000 buildings with about 188,000 structures burning to the ground.

A huge tsunami would strike isolated Pacific Ocean islands several hundred kilometres outside Tokyo, which are considered part of the municipality, but was not likely to cause damage or fatalities in the metropolis itself.

The biggest city in earthquake-prone Japan lies at the intersection of four tectonic plates and there is a 50 percent chance it will be struck by a magnitude-7.0 or higher quake in the next four years, according to the University of Tokyo's Earthquake Research Institute.

The government projection does not include fatalities and damage in outlying prefectures that make up Greater Tokyo, home to about 35.0 million people.

In 1923, Tokyo and surrounding areas were struck by a 7.9 magnitude quake that left more than 140,000 people dead and destroyed much of the city.