Tap water in Tokyo tested safe a day after showing elevated levels of radioactive iodine considered unsafe for infants. Stores were wiped out of bottled water Thursday because of the scare, and the government, while rationing water, milk and rice, is asking people not to stockpile goods.

Radiation has been leaking from a nuclear plant 140 miles northeast of Tokyo since it was struck by an earthquake March 11 and engulfed by the ensuing tsunami. Feverish efforts to get the plant’s crucial cooling system back in operation have been beset by explosions, fire and radiation scares.

On Thursday, two workers at the Fukushima Dai-ichi plant suffered injuries when their feet came in contact with radioactive elements while laying electrical cables in one unit, said Fumio Matsuda, a spokesman for the Nuclear and Industry Safety. NHK television reported that the workers’ legs were exposed as they worked in a basement flooded with radioactive water.

The two were being treated at a hospital. They were exposed to radiation levels between 170 to 180 millisieverts, less than the maximum amount of 250 millisieverts that the government allows for workers at the plant, Matsuda said.

That’s more radiation than many people will receive in a lifetime. It’s also enough to cause burns to the skin and damage to bone marrow. The spokesman said a third worker received a smaller exposure that did not require hospital care.

More than two dozen people have been injured trying to bring the Fukushima Dai-ichi plant under control.

The developments highlighted the challenges Japan faces after a magnitude 9 quake off Sendai triggered a massive tsunami. An estimated 18,000 people have been killed and hundreds of thousands have been left homeless as officials scramble to avert a major nuclear crisis.

Radiation has seeped into raw milk, seawater and 11 kinds of vegetables, including broccoli, cauliflower and turnips, grown in areas around the plant.

The U.S. and Australia were halting 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.

Concerns also spread to Europe. In Iceland, officials said they measured trace amounts of radioactive iodine in the air but assured residents it was “less than a millionth” of levels found in European countries in the wake of the 1986 Chernobyl disaster.

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.

In Tokyo, government spokesman Yukio Edano pleaded for calm. Officials urged residents to avoid panicked stockpiling, sending workers to distribute 240,000 bottles — enough for three small bottles of water for each of the 80,000 babies under age 1 registered with the city.

“Just because the readings were high there’s no immediate health hazard,” Edano said at a news conference Thursday. Asked what the government is doing about the shortage from the run on bottled water throughout Tokyo, Edano said, “For the great majority of the population other than the babies, the use of tap water would not be hazardous. Therefore, I hope those people without the babies would act calmly.”

That didn’t stop Reiko Matsumoto, mother of 5-year-old Reina, from rushing to a nearby store to stock up.

“The first thought was that I need to buy bottles of water,” the Tokyo real estate agent said. “I also don’t know whether I can let her take a bath.”

New readings showed Tokyo tap water was back to safe levels Thursday but the relief was tempered by elevated levels of the cancer-linked isotope in two neighboring prefectures: Chiba and Saitama.

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 feed infants tap water.

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

The limits refer to sustained consumption rates, and officials said parents should stop using tap water for baby formula but that it was no problem for infants to consume small amounts.

Still, shelves were bare in stores across Tokyo.

Maruetsu supermarket in central Tokyo sought to impose buying limits on specific items to prevent hoarding: only one carton of milk per family, one 5-kilogram bag of rice, one package of toilet paper, one pack of diapers, signs said. Similar notices at some drugs stores told women they could only purchase two feminine hygiene items at a time.

Kayoko Kano, a spokeswoman at Maruetsu headquarters, acknowledged that the earthquake and tsunami resulted in delays of some products.

A spokesman for Procter & Gamble Japan said its plant was fully operational but that rolling blackouts in Tokyo may be affecting distribution. “Consumers are nervous, and they may be buying up supplies,” Noriyuki Endo added.

Meanwhile, in the northeast, some 660,000 households still do not have water, the government said. Electricity has not been restored to some 209,000 homes, Tohoku Electric Power Co. said. Damage is estimated at $309 billion, making it the most costly natural disaster on record.

More than 19,000 U.S. Marines and sailors, with 20 ships and 140 aircraft, have delivered relief supplies, surveyed ports, conducted aerial searches and surveys and provided support to rescuers, the military said.

“This is without a doubt the most complex humanitarian mission ever conducted,” Vice Adm. Scott Van Buskirk, commander of the U.S. 7th Fleet, said in a statement Thursday. “It is not one disaster, but three: an earthquake, a tsunami, and a crisis at a nuclear power plant, made even more complicated by heavy weather that hampers visibility.”

NPR’s Jon Hamilton in Tokyo contributed to this report, which contains material from The Associated Press. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.