Singapore, which has limited food imports from Japan since the nuclear power plant began leaking radiation, says it has found radioactive contaminants in four vegetables imported from Japan.

The contaminants were found in vegetables imported from Chiba and Ehime, areas not as directly affected by the quake, as well as from Tochigi and Ibaraki, the Agri-Food and Veterinary Authority said on its website.

There were also unconfirmed reports that radioactive cesium 1.8 times higher than normal had been found in a green leafy vegetable grown in a research facility in Tokyo.

Kyodo news agency, citing the Tokyo metropolitan government, said Thursday that previous contamination had occurred in various vegetables near the troubled nuclear plant at Fukushima, but this was the first to be detected in a vegetable grown in the capital, more than 220 kilometres south of the plant.

The Singapore food authority said 161 samples of fresh foods as seafood, fruits, vegetables and meat have been tested. The latest results come from shipments imported to Singapore on Wednesday.

They showed that radioactive contaminants such as iodine 131 and cesium 134 had been found in Japanese wild parsley (mitsuba), rape seed plants (nanohana), Japanese mustard (mizuna) and perilla leaf.

Still, the threat level appears to be quite low. The authority said an adult would have to consume 184 kilograms of the foods to receive an exposure level equivalent to the normal background radiation that a person will be exposed to in a year.

Radiation fears remain high in Tokyo on Thursday, however, as water-distribution centres were set up for children under a year old and stores began to ration essentials such as milk, toilet paper and rice.

Iodine in tap water

Worries about health threats from airborne radioactive particles drifting to Japan's capital from the troubled nuclear plant at Fukushima increased after officials reported that radioactive iodine in tap water was measured at levels considered unsafe for babies over the long term.

"If you have a child under the age of one, you were allowed to go to the distribution centres to get a supply of bottled water for your infant," reporter Steve Futterman told CBC News from Tokyo.

Tokyo's 13 million residents are suffering the indirect effects of the March 11 earthquake and tsunami in northern Japan that did severe damage to the nuclear reactors operated by Tokyo Electric Power Co. at Fukushima.

Futterman said people were confused about the threat levels.

"What even made matters more confusing, in the middle of the day, Tokyo officials said, 'Well, you know, we have new tests, and the iodine levels [are] OK now for infants,'" he said.

"But the mothers I talked to said, 'Hey, we’re not going to take any chances.' They will give their children bottled water, and obviously parents of children above the age of one are trying to just give their children bottled water as well."

Households with infants were to get three half-litre bottles of water each — a total of 240,000 bottles — city officials said.

Double tolerable limits

Despite government appeals against panic, supermarkets and stores sold out of water, as residents crowded in to buy up what remained on the shelves.

Japan's major manufacturers and importers of bottled water announced they are increasing production.

Tokyo officials said Wednesday that 210 becquerels of radioactive iodine per kilogram of water had been found in water at the northeast Tokyo purification plant. The tolerable limit is 100 becquerels for infants and 300 becquerels for adults.

New readings Thursday showed the levels had returned to safe levels in Tokyo, but were high in two neighbouring prefectures — Chiba and Saitama.

On Thursday, officials warned that tap water in Kawaguchi City in Saitama just north of Tokyo also showed high levels of radiation.

The water problem in Tokyo, Japan's largest city, added to growing fears over the nation's food supply as workers at the Fukushima Daiichi nuclear plant 220 kilometres to the north struggled to regain control of the facility.

A child holds a bottle of water distributed at a nursery school in Tokyo on Thursday. Shops in Japan's capital have run out of bottled water after a warning that tap water was unsafe for infants. Kyodo/Reuters

Almost two weeks after the magnitude-9.0 quake, some 660,000 households still do not have running water in Japan's northeast, the government said Thursday. Electricity has not been restored to some 209,000 homes, Tohoku Electric Power Co. said.

The figures were a reminder of the grim humanitarian situation that hundreds of thousands continue to face in the wake of twin disasters that are proving to be the most costly natural disaster on record. Damages are estimated at up to $309 billion US, the government said.

As well, the number of dead and missing continued to rise: more than 10,000 dead, with another 17,440 missing, Japan's police agency said Friday, adding that the figures may include some overlap.

Radioactivity in vegetables

Fears about food safety began to spread overseas as radiation seeped into raw milk, seawater and 11 kinds of vegetables, including broccoli, cauliflower and turnips, from areas around the plant.

The latest data showed sharp increases in radioactivity levels in a range of vegetables. In an area about 40 kilometres northwest of the nuclear plant, levels for one locally grown leafy green called kukitachina measured 82 times the government limit for radioactive cesium and 11 times the limit for iodine.

Some countries have halted imports of Japanese dairy and produce from the region near the facility. Canada plans to upgrade controls on imports of Japanese food products, according to the Canadian Food Inspection Agency.

Unlike the United States, Canada isn't screening passengers or cargo arriving in Canada from Japan, a Health Canada spokeswoman said.

"However, we will continue to monitor the evolving situation related to the nuclear power plant in Japan."

Infants particularly vulnerable

Earlier this week, a detector in St. John's picked up minuscule traces of radiation believed to have come from the damaged nuclear power facilities in Japan.

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.

The amounts being reported in Tokyo 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, said Dr. Harold Swartz, a professor of radiology and medicine at Dartmouth Medical School in the U.S.

Meanwhile, the crisis in Japan has prompted a worldwide outpouring of aid. 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.

And in Tiverton, Ont., workers at the Bruce nuclear generating station are helping those who work at the crippled Fukushima nuclear plant in Japan.

Bruce Power and its employees raised more than $80,000 during a two-hour campaign Tuesday morning at the plant about 60 kilometres southwest of Owen Sound.

Even North Korea says it is helping: state media report leader Kim Jong Il has sent $500,000 US to ethnic Koreans in Japan.

With files from The Associated Press