Experts in Japan have warned that the chances of a powerful earthquake striking Tokyo in the next four years could be as high as 70%, a more alarming scenario for the city's 13 million people than predicted by the government.

The earthquake research institute at Tokyo University said that in the worst case, a quake of magnitude 7 would hit the southern part of metropolitan Tokyo by 2016, while the chances of a similar disaster occurring within 30 years are as high as 98%.

The government, by contrast, estimates the possibility of an earthquake that size striking the capital at 70% in the next three decades.

The warning comes less than a year after a magnitude-9 earthquake off the country's north-east coast triggered a tsunami that left about 23,000 people dead or missing.

The 11 March earthquake – the biggest in recorded history in Japan – and the tsunami that followed also triggered a meltdown at the Fukushima Daiichi nuclear power plant, forcing the evacuation of tens of thousands of residents.

Although newer buildings in Tokyo are built to withstand powerful earthquakes, a large quake in the city has the potential to cause widespread damage.

According to the government, a magnitude-7.3 earthquake would kill about 5,600 people, injure 159,000 and destroy 850,000 buildings.

Shinichi Sakai, an associate professor at the earthquake research institute, said that chances of a magnitude-7 earthquake striking Tokyo had increased since 11 March. "The government, individuals and corporations should make preparations for that now," he said.

Using data from Japan's meteorological agency, the institute said earthquakes of up to magnitude 6 had occurred five times more frequently than in normal years since the March disaster. The increased frequency has made it more likely that "the big one" could strike far sooner, it said.

The government said the researchers had reached their more worrying conclusion because they had used a different computer model to calculate the risks.

Days before the report was released, Tatsuo Hirano, the minister in charge of the recovery from the March disaster, said he was confident Tokyo could withstand a powerful quake. "Please rest assured and don't flee Tokyo," he said.

Hirano cited the lack of serious damage to Tokyo's buildings and transport infrastructure on 11 March as proof the city would be able to resist a large earthquake striking directly beneath or nearby.

But he added that data from multiple sources suggested there was a "high probability" that the city and the wider Kanto region were due for a powerful earthquake.

Last year's disaster caused widespread disruption to public transport in Tokyo, leaving tens of thousands of commuters stranded and unable to contact family and friends on overloaded mobile phone networks.

Japan accounts for about a fifth of the world's quakes of magnitude 6 or higher.

Safety standards for buildings improved after 1995, when an earthquake in Kobe killed more than 6,400 people, many of whom died in collapsed or burning buildings.