The United States became the first nation to block imports from Japan's radiation zone, saying it will halt milk, vegetables and fruit from areas near the tsunami-smashed nuclear plant because of contamination fears.
The Food and Drug Administration's decision to stop imports from four Japanese prefectures in the crisis-hit northeast crystallised international anxiety about the impact of the worst atomic crisis since Chernobyl in 1986.
Other nations may follow suit with formal bans. Some private importers have already stopped shipments from Japan anyway.
At the six-reactor Fukushima plant, crippled by a March 11 earthquake and tsunami, engineers are battling to cool reactors to contain further contamination and avert a meltdown.
Showing the widening problem, Japan said above-safety radiation levels had been discovered in 11 types of vegetables from the area, in addition to milk and water.
Officials still insisted, however, that there was no danger to humans and urged the world not to over react.
"We will explain to countries the facts and we hope they will take logical measures based on them," Japan's chief cabinet secretary Yukio Edano said.
The Asian nation's worst crisis since World War Two may have caused $300bn damage, sent shock waves through global financial markets, and left nearly 23,000 people dead or missing, mostly from flattened coastal towns.
More than a quarter of a million people are living in shelters, while rescuers and sniffer dogs comb debris and mud looking for corpses and personal momentoes.
Worsened by widespread ignorance of the technicalities of radiation, public concern is rising around the world and radioactive particles have been found as far away as Iceland.
Japan has already halted shipments of some food from the area and told people there to stop eating leafy vegetables.
Asian neighbours are inspecting imports for contamination, and Taiwan advised boats to stop fishing in Japanese waters.
Although there has been progress in restoring power to the Fukushima site 13 days after the accident, plant operator Tokyo Electric Power Co (TEPCO) said it needed more time before it could say the reactors were stabilised.