Japan's meteorological agency issued a warning for the Iwate, Miyagi and Fukushima prefectures, devastated by a huge quake and tsunami four months ago.

The Fukushima nuclear plant is being evacuated as a precaution, NHK TV reports. More than 14,000 people died as a result of the 9.0-magnitude earthquake and tsunami on 11 March.

Meteorologists warned of a possible surge of around 50cm (20in). There were no immediate reports of injuries or damage, according to NHK.

And Tokyo Electric Power Company (Tepco), which operates the crippled Fukushima Daiichi nuclear plant, said first reports indicated no fresh problems there.

The quake hit at 0957 local time (0057 GMT). The US Geological Agency estimated the depth at 10km (6.2 miles), with the epicentre in the same general area as the March quake.