Authorities in north-east Japan ordered a general evacuation and workers at the damaged Fukushima Daiichi nuclear plant took shelter after an earthquake triggered a new tsunami warning.
However, the tsunami warning was lifted after 90 minutes and the earthquake – with a magnitude of 7.1 – did little obvious damage.
Fukushima officials said the quake had no detectable effect at the plant.
Last month’s 9.0 earthquake set off a tsunami which devastated the region.
The earthquake – at a depth of 49km (32 miles) – struck off Japan’s north-east coast, close to the epicentre of the 11 March quake.
All seven of the workers at Fukushima Daiichi were safe, a spokesman for plant operator Tepco told a news conference in Tokyo.
“They have not been injured and they have all taken shelter in our seismic-resistant building. We are continuing to inject water, or we are continuing the injection operation at reactors 1, 2 and 3,” said the spokesman, whose name was not given.
The workers are trying to keep the damaged reactors cool to stop further releases of radioactive material.
Today’s quake struck at 2332 local time (1432 GMT)Â north of Fukushima, 40km offshore.
First reports said it had a magnitude of 7.4 but that was later revised downwards to 7.1, according to the US Geological Survey (USGS).
Last month’s earthquake had a magnitude of 9.0 and struck at 32km deep. (BBC)
