The operator of the Fukushima Dai-ichi plant said there were no abnormalities observed at the plant, though a swelling of the tide of up to 1 metre was detected offshore.

The plant was swamped by the 2011 tsunami, sending three reactors into meltdown and leaking radiation into the surrounding area. The plant is being decommissioned but the situation remains serious as the utility figures out how to remove still-radioactive fuel rods and debris and what to do with the melted reactor cores.

Plant operator Tepco said a pump that supplies cooling water to a spent fuel pool at the nearby Fukushima Dai-ni plant stopped working, but that a backup pump had been launched to restore cooling water to the pool.