However, Dr. James Cox, professor of radiation oncology at the M.D. Anderson Cancer Center in Houston, said the reported levels posed little or no health concerns.

Nonetheless, the Japanese government has banned the sale of raw milk from Fukushima Prefecture, where the Fukushima Daiichi plant is located, and prohibited the sale of spinach from neighboring Ibaraki Prefecture after finding levels of radioactive iodine and cesium higher than government standards, the country's Health Ministry reported. And officials in Fukushima halted the distribution of locally grown vegetables outside the prefecture.

The concerns about food may add an economic shock to the beating Japan has taken from the quake, which has so far left more than 23,000 dead, injured or missing.

Japanese officials reported levels of radioactive iodine in milk from four locations in Fukushima that ranged from about 20% over the acceptable limit to more than 17 times that limit. Testing at one location also found levels of cesium about 5% over the acceptable limit, the Health Ministry reported on March 20.

Fukushima, northeast of Tokyo, has Japan's fourth-largest amount of farmland and ranks among its top producer of fruits, vegetables and rice. Ibaraki, south of Fukushima, supplies Tokyo with a significant amount of fruits and vegetables and is Japan's third-largest pork producer.

After the Chernobyl nuclear disaster in 1986, tons of food had to be destroyed when radioactive debris fell on crops in large swaths of Eastern Europe and Scandinavia.

Hygiene expert Satoshi Takaya, who helped Japanese scientists prevent contaminated food from entering the country at that time, said the current situation is no Chernobyl - but he said the current crisis is sure to affect Japanese farmers.