Researchers say a major earthquake is far more likely to hit Tokyo in the next few years than the government estimates.
There is a 70 per cent chance a magnitude 7 quake will jolt the southern part of the Tokyo metropolitan area in the next four years, the University of Tokyo's Earthquake Research Institute said.
In contrast, the government estimates a 70 per cent probability of such an event in the next three decades.
A magnitude 9 quake, the strongest on record in Japan, and subsequent tsunami devastated the northeast coast last March.
It left up to 23,000 dead or missing and wrecked Fukushima Daiichi nuclear plant, triggering power shortages and a radiation leaks that caused mass evacuations and widespread contamination.
A government survey says a magnitude 7.3 quake centred in the north of Tokyo Bay would cause about 11,000 casualties and destroy around 850,000 buildings, though one of the University of Tokyo team said it was hard to predict the impact of a major quake on the city.
"The chance that a magnitude 7 earthquake will happen (in the area) has increased since the March quake," said Shinichi Sakai, an associate professor at the institute.
"At this time, the government, individuals and corporations should prepare for that."
A government official said the Tokyo University estimate was based on a different model from the one it uses.
The university calculations take account of the greater seismic activity since March, while the government uses older data.
There has been a fivefold increase in the number of quakes in the Tokyo metropolitan area since the March disaster, the research team said, basing its calculations on data from the Japan Meteorological Agency.
Japan, situated on the "Ring of Fire" arc of volcanoes and oceanic trenches that partly encircles the Pacific Basin, accounts for about 20 per cent of the world's earthquakes of magnitude 6 or greater.
A magnitude 7.3 quake hit central Japan in 1995, devastating the port city of Kobe.
It killed more than 6,400 people and caused an estimated $100 billion in damage.
The Great Kanto earthquake of 1923 had a magnitude of 7.9 and killed more than 140,000 people in the Tokyo area.
Seismologists have said another such quake could strike the city at any time.