Over the weekend spinach and milk produced near the nuclear plant was found to contain levels of radioactive iodine far higher than the legal limits.
However, senior government official Yukio Edano told a news conference that eating or drinking the contaminated food would not pose a health hazard. “I would like you to act calmly,” he said.
The World Health Organization said it had no evidence of contaminated food reaching other countries. However, China, Taiwan and South Korea have announced plans to toughen checks of Japanese imports.
Bad weather forced Japanese Prime Minister Naoto Kan to cancel a planned visit to emergency workers near the Fukushima plant.
It is also making the recovery work a much more difficult task.
Search-and-relief efforts in the prefecture of Miyagi, where the police chief believes the final quake-tsunami death toll could reach 15,000, have been delayed by driving rain.
“We basically cannot operate helicopters in the rain,” Miyagi official Kiyohiro Tokairin said.
“We have been using helicopters to deliver relief goods to some places but for today we have to switch the delivery to places that we can reach by road,” he said.
More than 350,000 people are still living in evacuation centres in northern and eastern Japan.