Japanese researchers have warned of a 70 percent chance that a magnitude-seven earthquake will strike Tokyo within four years, a report said Monday -- much higher than previous estimates.

Researchers at the University of Tokyo's earthquake research institute based the figure on data from the growing number of tremors in the capital since last year's March 11 earthquake off northeast Japan, the Yomiuri Shimbun reported.

According to the meteorological agency, an average of 1.48 earthquakes with magnitudes ranging from three to six have occurred per day in and near Tokyo since March.

That is around five times as many as before the disaster, the researchers said, according to the Yomiuri.

The Japanese government has forecast that the chance of a major quake of magnitude seven or more in the Tokyo region is 70 percent over the next 30 years.

Naoshi Hirata, one of the University of Tokyo researchers, said the results showed seismicity had increased in the area around capital, which was expected to lead to a higher probability of a major quake.

The 9.0-magnitude earthquake last year and the resulting tsunami left more than 19,000 people dead or missing and crippled the cooling systems at the Fukushima nuclear power station, causing meltdowns in some of its reactors.

The last time a "big one" struck Tokyo was in 1923, when the magnitude-7.9 Great Kanto Earthquake claimed more than 100,000 lives, many of them in fires. Previously, in 1855, the Ansei Edo quake also devastated the city.

Japan, located on the tectonic crossroads known as the "Pacific Ring of Fire" and dotted with volcanoes, is one of the world's most quake-prone countries, with Tokyo lying in one of its most dangerous areas.

The megacity sits on the intersection of three continental plates -- the Eurasian, Pacific and Philippine Sea plates -- which are slowly grinding against each other, building up enormous seismic pressure.