High levels of radioactive materials were detected on the Pacific seabed in a 300-kilometre stretch off a damaged nuclear plant in north-eastern Japan, news reports said Saturday.

The government said radioactive materials up to several hundred times higher than normal were found ranging from Miyagi prefecture to Chiba prefecture and warned that the contamination could affect the safety of seafood.

The science ministry detected iodine and caesium on the seabed at a dozen locations 15 to 50 kilometres from the coast between May 9 and 14, the Kyodo News agency reported.

Since the Fukushima Daiichi Nuclear Power Station was crippled by a magnitude-9 earthquake and tsunami on March 11, it has leaked radioactive materials into the environment.

In early April, plant operator Tokyo Electric Power Co started to dump low-level radioactive water into the ocean to make room for more highly contaminated water that had been leaking into the sea from the plant in Fukushima prefecture.

Greenpeace Japan said Thursday that it found radioactive materials above official limits for consumption in 14 of 21 samples of products including seaweed, shellfish and fish caught 22 to 60 kilometres from the plant.

Hidehiko Nishiyama, a spokesman for the government’s Nuclear and Industrial Safety Agency, has repeatedly said radioactive materials would significantly dilute by the time they were consumed by marine species.

But Greenpeace said it had observed a reconcentration of the substances in the ocean and called for long-term research.

More In: International | News