Japan warns of 'huge' earthquake after powerful tremor

Japan issued a special advisory on Monday warning of an increased risk of earthquakes at magnitude 8.0 or stronger, after a powerful jolt rattled the country's north and prompted a tsunami warning.

The Japan Meteorological Agency said in a statement that "the likelihood of a new, huge earthquake occurring is relatively higher than during normal times".

The warning for the northern region came a few hours after a 7.7-magnitude earthquake struck the area, shaking large buildings in the capital Tokyo, hundreds of kilometers from the epicentre.

The quake, which was initially estimated at magnitude 7.4 before being revised to 7.5 and again to 7.7, hit at 4:53 p.m. in Pacific waters off northern Iwate prefecture.

There were no immediate reports of serious injuries or significant damage, Chief Cabinet Secretary Minoru Kihara told a news conference.

A Cabinet Office official told a separate televised briefing that "while it is uncertain whether (another) major earthquake will actually occur, we ask that you take disaster preparedness measures based on the principle that you are responsible for your own safety".