Tokyo ( CNN ) -- The detection of high levels of radioactivity in certain Japanese foods -- and the nation 's subsequent clampdown on their sales -- signals the food safety situation is `` more serious '' than originally thought , a World Health Organization official said Monday . Peter Cordingley , the Manila-based spokesman for the WHO 's regional office for the Western Pacific , said his organization believes people in Japan `` have to be cautious '' about what they eat and drink . Besides causing devastation throughout northeast Japan , the 9.0-magnitude earthquake and subsequent tsunami on March 11 seriously damaged several reactors at the Fukushima Daiichi nuclear plant , leading to the release of an unspecified amount of radioactive material into the atmosphere . On Sunday , the sale of raw milk from Fukushima Prefecture and spinach from neighboring Ibaraki Prefecture were banned due to detected levels of radioactive iodine and cesium that surpassed government limits , Japan 's health ministry reported . And officials in Fukushima halted the distribution of locally grown vegetables outside the prefecture . Cordingley noted that , whereas fears initially were for produce within 30 kilometers ( 18 miles ) of the plant , cows ( and the milk they produce ) outside that radius and spinach from as far as 120 kilometers was being affected . `` Quite clearly , it is not what we thought in the early stages . It is more serious , '' he said . `` We have seen Japanese people in grocery stores paying close attention to where their produce is coming from , and we think this is a wise practice . '' Cordingley 's assessment -- and the Japanese health ministry 's move -- suggests that top world and national health agencies are definitely taking the issue seriously . And so are people in Japan . `` It does n't look like a short-term issue , '' said Phil Knall , who lives in Tokyo . `` I 'm definitely concerned about the food that is going to be shipped out from now . I 'm definitely thinking about it . '' 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 Sunday . And in Ibaraki , a major center of vegetable production , tests at 10 locations found iodine levels in spinach that ranged from 5 % over acceptable limits to more than 27 times that ceiling . At seven sites , levels of cesium grew from just above 4 % to nearly four times the limit . Iodine and cesium isotopes are byproducts of nuclear reactors like the ones that were damaged in the March 11 earthquake and tsunami that devastated the northern Japanese island of Honshu . While Iodine-131 has a radioactive half-life of eight days , cesium-137 's half-life is about 30 years . A few water samples taken in the area tested positive for iodine -- although far below levels of concern under Japanese law , according to the International Atomic Energy Agency website . The agency said it received reports from Japan 's government that six out of 46 samples tested positive for the iodine-131 radioactive isotope . The decision to prohibit food produce sales is another potentially devastating blow to a part of northeast Japan hit by the earthquake , tsunami and other potential fall-out from the Fukushima plant . 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 1986 nuclear plant disaster in Chernobyl -- then a part of the Soviet Union -- 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 . That means threatening the livelihood of people like Ukia Uchida , an 82-year-old woman whose family has farmed a plot in Shibayama for generations . `` Up until now , I thought everything was fine here , '' said Uchida . `` But to hear that some radiation has been found here is pretty upsetting . '' CNN 's Jo Kent , Catherine E. Shoichet , Steven Jiang , Martin Savidge , Paul Ferguson , Thom Patterson and Matt Smith contributed to this report .
A WHO official calls the food safety issue ` ` more serious '' than first thought . ` ` I ' m definitely thinking about '' possible radiation in food , a Tokyo says . High levels of radioactive iodine and iron have been found in milk and spinach . The two areas affected include some of Japan 's most productive regions .