Another major quake hit Japan around 17:16 local time. It was reported at magnitude 7.1, but later downgraded to 6.6.
The quake knocked out power to the Fukushima nuclear plant for a period of 15 minutes, when all workers were evacuated.
Over 200,000 houses in the area have lost power.
A tsunami warning was issued after the quake and people were told to seek higher ground. This alert was lifted after an hour.
It is the one-month anniversary of the massive earthquake. Today’s quake and similar activity on Thursday were attributed to aftershock from the first March 11 quake.
Meanwhile Japan is preparing to extend the evacuation zone as radiation spreads.