Updated at 3:55 p.m. ET
TOKYO - Radiation leaking from Japan's tsunami-damaged nuclear power plant has caused Tokyo's tap water to exceed safety standards for infants to drink, officials said Wednesday, sending anxiety levels soaring over the nation's food and water supply.
Residents cleared store shelves of bottled water after Tokyo Gov. Shintaro Ishihara said levels of radioactive iodine in tap water were more than twice what is considered safe for babies. Officials begged those in the city to buy only what they needed, saying hoarding could hurt the thousands of people without any water in areas devastated by the March 11 earthquake and tsunami.
"I've never seen anything like this," clerk Toru Kikutaka said, surveying the downtown Tokyo supermarket where the entire stock of bottled water sold out almost immediately after the news broke, despite a limit of two, two-liter bottles per customer.
The unsettling new development affecting Japan's largest city, home to around 13 million people, added to growing fears over the nation's food supply.
CBS News correspondent Bill Whitaker reports that the U.S. became the first nation to order a block on Japanese dairy and other produce from the region. Hong Kong officials later followed suit after news surfaced that radiation from the Fukushima Dai-ichi nuclear plant has seeped into raw milk, seawater and 11 kinds of vegetables, including broccoli, cauliflower and turnips, from areas around the plant.
Officials are still struggling to stabilize the nuclear plant, which on Wednesday belched black smoke from Unit 3 and forced the evacuation of workers, further delaying attempts to make needed repairs. The plant, 140 miles north of Tokyo, has been leaking radiation since the quake and tsunami knocked out its crucial cooling systems.
The crisis is emerging as the world's most expensive natural disaster on record, likely to cost up to $309 billion, according to a new government estimate. Police say an estimated 18,000 people were killed.
Concerns about food safety spread Wednesday to Tokyo after officials said tap water showed elevated radiation levels: 210 becquerels of iodine-131 per liter of water more than twice the recommended limit of 100 becquerels per liter for infants. Another measurement taken later at a different site showed the level was 190 becquerels per liter. The recommended limit for adults is 300 becquerels.
"It is really scary. It is like a vicious negative spiral from the nuclear disaster," said Etsuko Nomura, a mother of two children ages 2 and 5. "We have contaminated milk and vegetables, and now tap water in Tokyo, and I'm wondering what's next."
Infants are particularly vulnerable to radioactive iodine, which can cause thyroid cancer, experts say. The limits refer to sustained consumption rates, and officials urged calm, saying parents should stop giving the tap water to babies, but that it was no problem if the infants already had consumed small amounts.
They said the levels posed no immediate health risk for older children or adults.
"Even if you drink this water for one year, it will not affect people's health," Chief Cabinet Secretary Yukio Edano said.
Dr. Harold Swartz, a professor of radiology and medicine at Dartmouth Medical School in the U.S., said the radiation amounts being reported in the water are too low to pose any real risk, even to infants who are being fed water-based formula or to breast-fed infants whose mothers drink tap water.
Although the amounts are well above established limits, that doesn't automatically mean there's a health threat, he said.
"We live in a world that has natural background radiation that's many times greater than the amounts we're talking about here," Swartz said.
Still, because it's easy to avoid tap water, it makes sense for Japanese parents with infants to do so, he said.
Radioactive iodine is also short-lived, with a half-life of eight days the length of time it takes for half of it to break down harmlessly.
Richard Wakeford, a public health radiologist at the University of Manchester in Britain, blamed the spike in radiation on a shift in winds from the nuclear plant toward Tokyo. He predicted lower levels in coming days once the wind shifts back to normal patterns. "I imagine that bottled water is now quite popular in Tokyo," he said.
Tokyo's municipal government said it would distribute 240,000 bottles of water to households with infants. They estimated that there are currently 80,000 babies in the affected area, with each infant getting three bottles of 550 milliliters.
Edano pleaded with shoppers to restrict purchases of bottled water to the bare necessity, urging them to think of tsunami victims in need.
"We have to consider Miyagi, where there is no drinking water at all," he said, referring to a stricken region. "Under these conditions, we would appreciate it if people would avoid buying more water than they need."