One of Japan's six tsunami-crippled nuclear reactors appears to be stabilising, following efforts by engineers and firefighters.

Engineers reported some success on Saturday after fire engines sprayed water for hours on the number three reactor at the ravaged Fukushima Daiichi nuclear complex.

"The situation there is stabilising somewhat," Yukio Edano, the chief cabinet secretary, told a news conference.

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The number three reactor is widely considered the most dangerous at the plant because it uses highly toxic plutonium.

The IAEA says radiation levels outside the plant are safe, but despite signs of progress, the crisis looks far from resolved.

Engineers are using a 1.5km power cable in an attempt to re-start water pumps that would cool overheating nuclear fuel rods and prevent a deadly radiation leak.

Engineers fixed the power cable to the number two reactor but have yet to turn on its coolers.

Four of the worst-hit reactors in the complex should have electricity by Sunday, Japan's Nuclear and Industrial Safety Agency said, a potentially crucial milestone in the world''s worst nuclear accident in 25 years.

They plan to test power in reactors one, two, three and four on Sunday, Hidehiko Nishiyama, deputy director general of the agency, said.

Radiation levels

Thousands living outside the danger zone but within a 30km radius are heeding a government request to stay indoors and close all windows, doors and vents, but face dwindling supplies of heating fuel, food and water.

Japan has also reported its first contamination of food since the  March 11 earthquake and tsunami that left nearly 18,000 people dead or missing and triggered the nuclear emergency.

Authorities ordered a halt to all food product sales from Fukushima prefecture, said the International Atomic Energy Agency (IAEA), warning that radioactive iodine found in food can pose a short-term health risk.

Radiation levels in milk from a Fukushima farm about 30km from the plant, and spinach grown in the neighbouring prefecture of Ibaraki were found to exceed government limits.

Faint radiation was also found in tap water in Maebashi, 100km north of Tokyo, the Kyodo news agency reported.

Chief Cabinet Secretary Edano told reporters before the IAEA warning that higher radiation levels posed no risk to human health, but the findings are sure to heighten scrutiny of Japanese food exports.

Restaurants in Singapore are already considering importing sushi, sashimi and other Japanese ingredients from elsewhere.

Public apology

Tokyo Electric Power Co, the operator of the 40-year-old Fukushima plant, is facing mounting criticism in Japan, including questions over whether it hesitated too long before dousing the reactors with seawater, which permanently damages them.


Al Jazeera's Harry Fawcett reports from Morioka

On Saturday, its president issued a public apology for "causing such great concern and nuisance".

Plant officials say a last resort, if all else fails, would be to bury the sprawling old plant in sand and concrete to prevent a catastrophic radiation release.

The method was used at the Chernobyl reactor in 1986, the scene of the world's worst nuclear reactor disaster.

The operation to avert large-scale radiation has largely overshadowed the humanitarian crisis caused by the 9.0-magnitude quake and 10-metre tsunami.

Some 390,000 people, many elderly, are homeless, living in shelters in near-freezing temperatures in northeastern coastal areas and food, water, medicine and heating fuel are in short supply.

Nearly 290,000 households in the north still have no electricity and about 940,000 lack running water.

Aid groups say most victims are getting help, but there are pockets of acute suffering.

Source: Al Jazeera and agencies