Workers at the Fukushima Daiichi nuclear power plant
Japan will have to review its nuclear power policy, its top government spokesman said, as fear of radiation from an earthquake-damaged nuclear complex spread both at home and abroad.
Engineers are trying to stabilise the six-reactor nuclear power station in Fukushima, 240 km (150 miles) north of the capital, two weeks after an earthquake and tsunami battered the plant and devastated north-eastern Japan, leaving about 27,400 people dead or missing.
"It is certain that public confidence in nuclear power plants has greatly changed," Chief Cabinet Secretary Yukio Edano told Reuters late on Thursday.
"In light of that, we must first end this situation and then study from a zero base."
Japan's 55 nuclear reactors have been providing about 30 percent of the nation's electric power. The percentage had been expected to rise to 50 percent by 2030, among the highest in the world.
The 9.0 magnitude earthquake on March 11, the tsunami it triggered and the nuclear crisis they caused have brought Japan its darkest days since World War Two.
Explosions in three reactors at the Fukushima Daiichi power station last week made this the world's worst nuclear crisis since Chernobyl and raised fears of a catastrophic meltdown.
While that has not happened, radiation has been leaking and four of the plant's reactors are still volatile.
Engineers from the plant's operator, Tokyo Electric Power Co (TEPCO), have been making some progress in restoring power and regaining control, but periodic emissions of smoke and steam revive fears of a nuclear nightmare.
"It's still a bit early to make an exact time prognosis, but my guess is in a couple of weeks the reactors will be cool enough to say the crisis is over," said Peter Hosemann, a nuclear expert at the University of California, Berkeley.
"It will still be important to supply sufficient cooling to the reactors and the spent fuel pools for a longer period of time. But as long as this is ensured and we don't see any additional large amount of radioactivity released, I am confident the situation is under control."
Three workers replacing a cable to help cool a reactor were injured by standing in radioactive water. Two were taken to hospital with burns, nuclear safety agency officials said.
On Wednesday, Tokyo's 13 million residents were told not to give tap water to babies after contamination hit twice the safety level this week. But it dropped back to safe levels the next day.
Despite government appeals for people not to panic, many shops saw bottled water supplies flying off the shelves.
Radiation above safety levels has also been found in milk and vegetables from Fukushima and the Kyodo news agency said radioactive caesium 1.8 times higher than the standard level was found in a leafy vegetable grown at a Tokyo research facility.
Alarm has spread, particularly among Japan's neighbours.
Singapore said on Thursday it had found radioactive contaminants in four samples of vegetables from Japan.
Earlier, it and Australia joined the United States and Hong Kong in restricting food and milk imports from the zone, while Canada became the latest of many nations to tighten screening.
Tiny radiation particles have also spread on the wind and been found as far away as Iceland, although experts say they are not dangerous.
Japan has urged the world not to overreact, and plenty of experts appeared to back that up.
Aftershocks are still jolting the country. Several shook Tokyo on Thursday.