Hundreds of thousands of survivors are still camped out in temporary shelters. Some 660,000 households do not have water more than 209,000 do not have electricity. Damage could rise as high as $310 billion, the government said, making it the most costly natural disaster on record.

The total death toll from the disaster could rise much higher as the National Police Agency said more than 17,400 people are still missing. Those tallies may overlap, but police from one of the hardest-hit prefectures, Miyagi, estimate that the deaths will top 15,000 in that region alone.

Japan has been grappling with an avalanche of miseries that began with the March 11 quake, which ravaged the northeastern coast and damaged the critical cooling system at the Fukushima Dai-ichi nuclear power plant, located 140 miles (220 kilometers) northeast of Tokyo.

As operators of the Fukushima plant struggled to get the cooling system operating again, radiation has seeped into the air and water, stoking fears about the safety of Japan’s food and water supply. Radiation has been found in raw milk, seawater and 11 kinds of vegetables, including broccoli, cauliflower and turnips, grown in areas around the plant.

Radioactive iodine is short-lived, with a half-life of eight days — the length of time it takes for half of it to break down harmlessly. However, experts say infants are particularly vulnerable to radioactive iodine, which can cause thyroid cancer.

The U.S. and Australia have halted imports of Japanese dairy and produce from the region, Hong Kong said it would require that Japan perform safety checks on meat, eggs and seafood, and Canada said it would upgrade controls on imports of Japanese food products. Singapore, too, has banned the sale of milk, produce, meat and seafood from areas near the plant.

In Tokyo, residents stripped store shelves of bottled water and some other basic necessities after authorities said radioactive iodine in the tap water was more than twice what is considered safe for babies to drink.

"The first thought was that I need to buy bottles of water," said Reiko Matsumoto, a real estate agent and mother of a 5-year-old, who rushed to a nearby store to stock up on supplies. "I also don’t know whether I can let her take a bath."

Tests conducted Thursday showed the levels in the city’s water fell to acceptable limits for infants, but shot up in neighboring regions.

In Tokyo, government spokesman Yukio Edano pleaded for calm over the water contamination, and said the government was considering importing bottled water from other countries to cover any shortages. Officials urged residents to avoid panicked stockpiling and the city distributed bottled waters to families with infants.

New readings Thursday showed the city’s tap water was back to levels acceptable for infants, but the relief was tempered by elevated levels of the isotope in two neighboring prefectures: Chiba and Saitama. A city in a third prefecture, just south of the plant, also showed high levels of radioactive iodine in tap water, officials said.

Tap water in Kawaguchi City in Saitama, north of Tokyo, contained 210 becquerels of radioactive iodine — well above the 100 becquerels considered safe for babies but below the 300-becquerel level for adults, Health Ministry official Shogo Misawa said.

In Chiba prefecture, the water tested high for radiation in two separate areas, said water safety official Kyoji Narita. The government there warned families in 11 cities in Chiba not to give infants tap water.

"The high level of iodine was due to the nuclear disaster," Narita said. "There is no question about it."

Radiation levels also tested dangerously high in Hitachi in Ibaraki prefecture, about 70 miles (120 kilometers) south of the Fukushima plant, city water official Toshifumi Suzuki said.

In Fukushima, plant operators were still struggling to get the cooling system operating again. Lighting was restored Thursday to the central control room at Unit 1 for the first time since the tsunami, but two workers were treated at a hospital after stepping into radiation-contaminated water.

The water seeped over the top of their boots and onto their legs, said Takashi Kurita, spokesman for plant owner Tokyo Electric Power Co.

The men will be transferred to a radiology medical institute Friday, said Hidehiko Nishiyama, another nuclear agency spokesman. Their injuries were not life-threatening.

Associated Press writers Mari Yamaguchi, Elaine Kurtenbach and Yuri Kageyama contributed to this report.