Japan's main island of Honshu was hit by another earthquake today at 23:32 local time (14:32 GMT), which reportedly measured between 7.1 and 7.4 in magnitude.
The epicentre was 25 miles below ground and around 60 miles from Sendai - the town which was devastated by last month's earthquake. Fukushima, the location of the nuclear power plant which has only just been plugged, is 90 miles away.
The Japanese authorities have ordered an evacuation from the Fukushima plant, and the wider coastal area. Buildings in Tokyo, which is almost 200 miles away from the epicentre, were reportedly shaken by the force of the quake.
A tsunami warning has been issued, but only as a precautionary measure.
Japan is only beginning to recover from the previous earthquake, which was a magnitude 9.0 and caused a tsunami which destroyed whole towns.