Japan’s science ministry says 8 per cent of the country’s surface area has been contaminated by radiation from the crippled Fukushima nuclear plant.
It says more than 30,000 square kilometres of the country has been blanketed by radioactive caesium.
The ministry says most of the contamination was caused by four large plumes of radiation spewed out by the Fukushima nuclear plant in the first two weeks after meltdowns.
The government says some of the radioactive material fell with rain and snow, leaving the affected areas with accumulations of more than 10,000 becquerels of caesium per square metre.
Last week tests found unsafe levels of radioactive contamination in recently harvested rice from the Fukushima region.
The levels of radioactive caesium were measured at 630 becquerels per kilogram, above the maximum allowable level of 500 becquerels.
Officials from Fukushima prefecture have now asked all rice farmers in the district to suspend shipments.
There have been a series of scares over radiation in food in Japan in recent months; in products such as beef, mushrooms and green tea, but never before in the country’s staple, rice.
Authorities have also begun testing soil in some Tokyo playgrounds and schools for traces of radioactive contamination.
Many people in Japan have purchased their own Geiger counters to monitor radiation levels around them.
The Fukushima plant went into meltdown after a massive earthquake and tsunami hit the country in March.
