Japanese authorities advised against allowing infants to drink tap water in Tokyo due to raised radiation levels and the United States became the first nation to block some food imports from Japan.
The crisis at the tsunami-smashed nuclear power plant, 250 km (150 miles) north of the Japanese capital, appeared far from over with workers attempting to gain control ordered to leave the site after black smoke began rising from one of its six reactors.
The plant was crippled by a 9.0 magnitude earthquake and tsunami on March 11. Some 23,000 people have been left dead or missing.
Tokyo authorities said water at a purification plant for the capital of 13 million people had 210 becquerels of radioactive iodine - more than twice the safety level for infants.
"This is without doubt, an effect of the Fukushima Daiichi plant," a Tokyo metropolitan government official said, referring to the nuclear power station.
Tokyo governor Shintaro Ishihara, however, said the radiation level posed no immediate health risk and water could still be used.
"But for infants under age one, I would like them to refrain from using tap water to dilute baby formula," he said.
International concerns about food safety are growing, with the United States the latest to impose controls. The U.S. Food and Drug Administration said it was stopping imports of milk, vegetable and fruit from four prefectures in the vicinity of the crippled nuclear plant.
South Korea may be next to ban Japanese food after the world's worst atomic crisis since Chernobyl in 1986. France this week asked the European Commission to look into harmonizing controls on radioactivity in imports from Japan.
Food made up just 0.6 percent of Japan's total exports last year.
Authorities 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 major 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, who has been the government's public face during the disaster, told a news conference.
Japan has already halted shipment of some food from the area and told people there to stop eating leafy vegetables. Asian neighbors are inspecting imports for contamination, and Taiwan advised boats to stop fishing in Japanese waters.
At the Fukushima plant, engineers are battling to cool reactors to contain further contamination and avert a meltdown.
But they were ordered out on Wednesday when black smoke began rising from the No.3 reactor, the plant's operator, Tokyo Electric Power Co, said. It said it did not know what was causing the smoke.
The Asian nation's worst crisis since World War Two may have caused $300 billion damage and has sent shock waves through global financial markets.
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 mementoes.
Drama at Fukushima
Technicians working inside an evacuation zone around the plant have successfully attached power cables to all six reactors and started a pump at one to cool overheating fuel rods.
As well as having its workers on the front line in highly dangerous circumstances, TEPCO is also facing accusations of a slow disaster response and questions over why it originally stored more uranium at the plant than it was designed to hold.
Vienna-based U.N. watchdog, the International Atomic Energy Agency (IAEA), expressed concern about a lack of information from Japanese authorities. It cited missing data on temperatures of spent fuel pools at the facility's reactors 1, 3 and 4.
"We continue to see radiation coming from the site ... and the question is where exactly is that coming from?" said a senior IAEA official, James Lyons.
U.S. Defense Secretary Robert Gates said he was concerned about radioactive fallout affecting the U.S. 55,000 troops in and around Japan, many involved in a massive relief operation for Washington's close ally. "We're also deeply concerned about the wellbeing of our Japanese allies," he said.
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.
Experts said tiny traces of radioactive particles, measured by a network of monitoring stations as they spread eastwards from Japan across the Pacific, North America, the Atlantic and to Europe, were far too low to cause any harm to humans.
"It's only a matter of days before it disperses in the entire northern hemisphere," said Andreas Stohl, a senior scientist at the Norwegian Institute for Air Research
The Japan crisis has dealt a blow to the nuclear power industry around the world. Italy became the latest nation to re-assess its program, announcing a one-year moratorium on site selection and building of plants.
Crisis in the world's third-biggest economy - and its key position in global supply chains, especially for the auto and technology sectors - has added to global market jitters, also affected by conflict in Libya and unrest in the Middle East.
Asian shares fell on Wednesday, with Tokyo's Nikkei ending 1.65 percent down as investors took profits from a two-session bounce. Japanese stocks are about 8 percent below their close on the day the big quake struck.
Toyota said it would delay the launch in Japan of two additions to the Prius line-up, a wagon and a minivan, from the originally planned end-April due to production disruptions.
The tsunami and earthquake are the world's costliest ever natural disaster, with the government estimating damage at 15-25 trillion yen ($185 billion-$308 billion).
The upper end of that range would equate to about 6 percent of Japan's gross domestic product.
The official death toll has risen to 9,199, but with 13,786 people still reported missing, it is certain to rise.
There are reports dozens of survivors, mostly elderly, have died in hospitals and evacuation centers due to a lack of proper treatment, or simply because of the cold.
Desperate municipalities are digging mass graves, unthinkable in a nation where the dead are usually cremated and their ashes placed in stone family tombs near Buddhist temples.
"This is a special measure, but there is nothing much else we can do," said Kazuhiko Endo, an official in Kamaishi town, where a mass burial is planned on Friday for 150 unidentified people.
"More than a week has passed since we placed them in morgues and we don't know if they can be identified."