TOKYO — A new study is warning that Tokyo has a 70 per cent chance of being hit by a powerful magnitude-7 earthquake within four years.

The study published Monday by University of Tokyo seismologists based the warning on an increase in seismic activity in the region since last year's March 11 disaster, when a magnitude-9 quake and subsequent tsunami along Japan's northern coast left nearly 20,000 people dead or missing.

The group said the number of moderate earthquakes in Tokyo increased sevenfold in the six-month period after March 11 compared with the previous six months, leading to the prediction.

Japan is one of the world's most earthquake-prone countries. Tokyo's last major quake was the 1923 Great Kanto Earthquake that killed 140,000 people.