At a downtown grocery store, a line of anxious mothers cleaned the shelves of bottled water seven minutes after the doors opened. At an organic farm on the city’s outskirts, a group tested spinach with a hand-held radiation detector. And at the prime minister’s headquarters, the chief cabinet secretary announced that Japan is considering importing drinking water.

As emergency crews battled Thursday to contain nuclear fallout from the earthquake-hit Fukushima Daiichi power plant in northeast Japan, a nervous uncertainty spread as far away as Tokyo, 150 miles to the southwest, as radiation was reported in parts of the food chain and millions tried to understand the implications.

In Vienna, the International Atomic Energy Agency reported Thursday that Japanese scientists have found “measurable concentrations” of radioactive iodine-131 and cesium-137 in samples of seawater collected off the Fukushima prefecture coast.

“The iodine concentrations were at or above Japanese regulatory limits, and the cesium levels were well below those limits,” the IAEA said on its Web site. The samples were gathered Tuesday and Wednesday at several points 18.6 miles from shore, the U.N. nuclear watchdog agency said.

A day after Tokyo officials warned of elevated iodine levels in the city’s tap water and the national government restricted shipment of 11 leafy vegetables in several prefectures, residents scrambled to stock up on the essentials, which are now in short supply.

Tokyo officials distributed 240,000 bottles of water to households with infants, who are more vulnerable to radioactive iodine-131. The U.S. Embassy handed out to American citizens potassium iodide pills, which can block radioactive iodine from building up in the thyroid gland.

“If the situation isn’t better in one week, I actually might have to move in with my parents,” said Yuki Ochiai, 32, mother of an 8-month-old girl who was among two dozen customers in line at the Tokyu grocery store 20 minutes before it opened. “My husband is already encouraging me to leave.”

As residents fretted, the number of deaths from the March 11 earthquake and tsunami officially topped 10,000, the National Police Agency said Friday. More than 17,000 people remain missing.

Two weeks after the quake, Japan Prime Minister Naoto Kan is scheduled to address the nation at 7:30 p.m. Friday, his spokesman said.

Meanwhile, the struggle to prevent more radiation from escaping the nuclear plant continued. Engineers hooked up lighting to a control room at the unit 1 reactor Thursday — an incremental, but hopeful, step toward cooling overheated spent fuel rods. At the unit 3 reactor, workers prepared to test a cooling pump that would allow them to pour in fresh rainwater instead of less effective seawater.

But there were setbacks. Three workers suffered radiation burns after stepping in contaminated water while attempting to lay electrical wiring at one of the buildings. Two of the workers, exposed to 170 to 180 millisieverts of radiation, were hospitalized, said Chief Cabinet Secretary Yukio Edano, who did not disclose the status of the third employee. The Associated Press quoted Fumio Matsuda, a spokesman for the Nuclear and Industrial Safety Agency, as saying that radiation levels of 170 to 180 millisieverts were well below the maximum 250 millisieverts allowed for workers.

Officials said Friday they are investigating possible damage to the reactor vessel at unit 3 that could be allowing dangerous radiation to leak into the atmosphere.

Government authorities said they are analyzing the reactor’s vessel, pipes and valves for potential damage that could be causing a leak. That reactor is considered particularly dangerous because it is the only one that burns mox fuel, a combination of plutonium and uranium that is hotter than conventional uranium reactors.

“Looking at the data, we believe the No. 3 vessel still has the capacity to contain radioactive material,” Hidehiko Nishiyama, deputy director-general of the Japan Nuclear and Industrial Safety Agency, said at a news conference. “But we have to investigate … the possibility the No. 3 reactor has sustained damage.”

The setback is the latest in a fitful effort to contain nuclear fallout at the Daiichi power plant. Crews have attached power cables to try to restore electricity, but only two of the six facility’s six reactors have successfully been put into cold shutdown. Twice this week, workers were evacuated after smoke was seen rising from the buildings, though officials later said the smoke was caused by steam that is not harmful.

The nervous uncertainty over the food chain Thursday sent people sifting through information about the complicated and rapidly changing problem. In Chiba and Saitama, two prefectures neighboring Tokyo, officials discovered iodine levels exceeding the legal limit for infants. Yet Tokyo’s water, which had tested high a day earlier, showed a decrease Thursday.

For some, the brief water warning was a tipping point, a sign that the environment had become a threat. At the Tokyu grocery, an employee opened the store doors at 10 a.m. and a half-dozen pregnant women and young mothers rushed to the far aisle.

Within seven minutes, all 80 two-liter bottles were gone. Ochiai, cradling her daughter, held two of them. Her parents, who live in Hokkaido, a northern island, were sending 12 more bottles of water by airmail, she said.

“I actually feel sorry standing here with my two bottles of water,” Ochiai said. “All these other mothers are here now, and they are too late.”

As parents worried about supply, farmers brooded over the demand for their food, tainted by the government’s advisory that residents not eat 11 leafy vegetables grown in prefectures near the Daiichi facility, citing elevated levels of radioactive materials in them.

The advisory has left farmers nationwide wondering about the effect on their livelihood as consumers weigh the risks.

At a spinach farm in Chiba, about 11 / 2 hours outside Tokyo, the proprietor, Masayuki Kumate, 45, looked on as Sumito Hatta, a food researcher, used a dosimeter to take a radioactivity reading of a lone row of green plants sprouting from the dark brown soil.

Kumate shook his head. Although Chiba officials had not banned any produce, Kumate said he has “been worried since Day One” of the disaster.

“It’s so clear what was going to happen,” he said of the nuclear fallout. “For Fukushima farmers, it is impossible [to recover]. The soil is contaminated. They will have to get rid of that before they start again. It takes a very long time. It will be a very big problem.”

Hatta and a friend, Shinya Takeda, started a blog and a Facebook page dedicated to informing the Japanese people and the world about the plight facing Japan’s farmers and asking for donations.

Japan’s Ministry of Agriculture, Forestry and Fisheries sent a letter to banks this week encouraging them to provide loans to farmers seeking to rebuild. And the government has pledged that the Tokyo Electric Power Co., which operates the nuclear plant, will provide stipends to farmers whose crops have been contaminated.

“The farmlands that were soaked with saltwater will not be revived as farmland,” the Facebook page reads. “This reality is another destruction for the farmers. . . . Now people in Japan are buying up all food at supermarkets and oil at gas stations due to the anxiety. Our food sovereignty is in great danger.”

Special correspondents Akiko Yamamoto and Kyoko Tanaka contributed to this report.