However, no tsunami warning was issued following the 8:56 am quake.

Ibaraki is one of the areas severely damaged in the March 11 catastrophic quake, and is located south of Fukushima Prefecture, the home of the troubled nuclear power plant.

In another development, two workers at Japan's damaged Fukushima Daiichi nuclear power plant have been taken to hospital after being exposed to high levels of radiation.

The pair had been attempting to restore the cooling system in reactor 3 which was damaged by the quake on March 11.

Several workers have now been hurt on the site, an indication of the scale of the task facing them.

Radiation levels in Tokyo's water supply have now fallen, but remain high in other areas of northern Japan.

The official death toll from the magnitude 9.0 quake and subsequent tsunami has now risen to 9,523. Another 16,094 people are listed as missing.

Japan's nuclear safety agency said three workers had been injured when their feet came into contact with radiation-contaminated water while laying cables in the turbine area of reactor 3.