It was earlier reported that radioactive iodine in sample water taken at 100 meters from the shoreline in the vicinity of the nuclear reactors was 29.8 times the permissible limits.

Residents in Tokyo were warned on Wednesday not to let infants drink tap water due to high iodine concentrations, but said on Thursday the iodine in the water had returned to safe levels. Experts say there is little chance of the situation at the plant to the point that there is an explosion like at Chernobyl in April 1986, and pollution should also not reach similar levels.

"It is very unlikely that Fukushima would develop into an accident like Chernobyl," International Atomic Energy Agency chief Yukiya Amano said.

A powerful earthquake and ensuing tsunami that hit Japan on March 11 triggered a number of explosions at Fukushima, spreading fears of massive radioactive contamination.

More than 9,000 people have been confirmed dead in the twin disasters, but more than 16,000 are reported and officials say the final death toll is likely to top 20,000.