Tokyo residents have been warned not to give babies tap water because of radiation leaking from a nuclear plant crippled in the earthquake and tsunami that devastated northeast Japan, in the world's costliest natural disaster. The UN atomic agency said there had been some positive developments at the Fukushima nuclear plant 250 km north of Tokyo but the overall situation remained serious. Some countries have started blocking imports of produce from Japan, fearful of radiation contamination. The first official estimate put the cost from the 11 March disaster at more than $300 billion, dwarfing losses from both the 1995 Kobe quake and Hurricane Katrina, which swept through New Orleans in 2005, making it the world's costliest natural disaster. The plant, battered by a 9.0 magnitude earthquake and tsunami that has left 23,000 people dead or missing, has still not been brought under control, and workers were forced away from the complex when black smoke began rising from one of its six reactors. "There are some positive developments related to the availability of electrical power...although the overall situation remains of serious concern," Graham Andrew, a senior official of the International Atomic Energy Agency (IAEA), told a news conference. Tokyo authorities said on Wednesday that 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. Tokyo Governor Shintaro Ishihara said that level posed no immediate risk. "But, for infants under age one, I would like them to refrain from using tap water to dilute baby formula." As concern grew over the risk to food safety of radiation from the nuclear plant, the United States became the first nation to block some food imports from the disaster zone. It is stopping imports of milk, vegetables and fruit from four prefectures in the vicinity of the plant. Hong Kong, a major importer of Japanese food, also banned produce and milk imports from the disaster zone. Japan's Jiji news agency said Hong Kong authorities had found radioactivity levels in spinach and turnip samples up to 10 times above the safety limit. France this week asked the European Commission to look into harmonizing controls on radioactivity in imports from Japan, after the world's worst atomic crisis since Chernobyl in 1986. Authorities have said above-safety radiation levels had been discovered in 11 types of vegetables from the area, in addition to milk and water, and have halted shipments of some food and told people there to stop eating leafy vegetables. Chief cabinet secretary Yukio Edano, the government's public face during the disaster, urged the world not to overreact. Edano also said an exclusion zone around the plant did not need to be expanded and he urged Tokyo residents not to hoard bottled water, a plea that fell on deaf ears, with many shops quickly selling out of supplies. "If this were temporary, I wouldn't be so worried. If this is long term, I think we have a lot to worry about," said Riku Kato, father of a one-year-old baby. Physicians for Social Responsibility, a US anti-nuclear group, disputed the food safety assurances and called for a more strict ban on sales of exposed food. "There is no safe level of radionuclide exposure, whether from food, water or other sources. Period," said physician Jeff Patterson, a former president of the group. The Asian nation's worst crisis since World War Two has sent shock waves through global financial markets. The damage estimate of $300 billion could go higher as it does not include losses in economic activity from planned power outages or the broader impact of the nuclear crisis. The 1995 Kobe quake cost $100 billion, while Hurricane Katrina caused $81 billion in damage. 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 mementos. POWER CABLES ATTACHED Technicians have successfully attached power cables to all six reactors at the Fukushima plant 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, Tokyo Electric Power Co. (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. The IAEA has expressed concern about a lack of information from Japanese authorities, citing missing data on temperatures of spent fuel pools at the facility's reactors 1, 3 and 4. Japan Nuclear Safety Commission Chairman Haruki Madarame said the government was "swiftly releasing information that is certain and not speculative" within Japan, but acknowledged it is behind in releasing information to foreign countries." Experts have said tiny 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 Andrea Stahl, a senior scientist at the Norwegian Institute for Air Research. GLOBAL IMPACT The Japan disaster 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. The death toll from the disaster has risen to 9,523, but with 16,094 people still missing, it is certain to rise. There are reports that dozens of survivors, mostly elderly, have died in hospitals and evacuation centers from a lack of proper treatment, or simply because of the cold.
