The operator of the stricken Fukushima nuclear power plant says engineers have bored holes in the roofs of the buildings housing reactors 5 and 6 to avoid a potential gas explosion.
"Due to fears of a hydrogen gas build-up from spent fuel pools in reactors 5 and 6, TEPCO has bored three 3.0-7.5 centimetre holes in the roofs of the reactor buildings," a spokesman for the company said.
Engineers restored limited power to the plant on Saturday and the nuclear safety agency said workers were on the brink of resuming a connection to the power grid.
With power back up, the radiation-suited Fukushima engineers will be able to get vital cooling systems online. In the meantime, they have been dumping water by hose and by air on the reactors to avert a feared meltdown.
The lack of power has sent the temperatures of fuel rods - both in the reactors and in separate containment pools - soaring as fast-evaporating coolant water leaves them exposed to the air.
The natural disaster on March 11 led to a series of hydrogen explosions and fires at buildings housing the reactor units, stoking anxiety among governments and the public worldwide and contributing to turmoil on financial markets.
But in a televised address Friday evening, Prime Minister Naoto Kan promised the traumatised nation: "We will overcome this tragedy and recover... We will once more rebuild Japan."
Recalling Japan's recovery from the ashes of World War II, Kan promised "firm control" of the disaster and said: "We are in a situation in which this crisis is truly testing us as a people."
Japan and its G7 economic allies on Friday intervened jointly in world currency markets for the first time in a decade to calm the turmoil, pushing down the yen as intended and helping to lift battered Tokyo shares.
Japan's nuclear agency has hiked the Fukushima accident level to five from four on an international scale measuring up to seven, an admission the crisis now at least equals the 1979 Three Mile Island accident in Pennsylvania.
Japanese and foreign experts are stressing that there is only a very low risk of radiation contamination beyond a 20-kilometre exclusion zone, and say the accident does not compare to the Chernobyl disaster in 1986.
However, fears of radiation hold a terrifying grip in the only country to have suffered a nuclear attack, when US atom bombs in 1945 finally brought Japan to surrender in World War II.
The threat of a nuclear disaster carries a particular resonance for Ayako Ito, who at 84 is old enough to recall the dropping of the US bombs on the cities of Hiroshima and Nagasaki.
"The most difficult part is that you cant see it but people can just disappear like that," she told AFP at her hillside home in Kamaishi, one of the towns that bore the full force of the towering 10-metre tsunami.
"We're already not eating or drinking, and now this is happening to us? It's very difficult," she said.
A major international relief operation is under way for the homeless and millions left without water, electricity, fuel or enough food in Japan's northeast.
But thick snow has covered the wreckage littering obliterated towns and villages, all but extinguishing hopes of finding anyone else alive in the debris and deepening danger and misery for survivors.
The absence of electricity in the affected areas means little access to television news and newspapers are very hard to come by. So news about the nuclear crisis is often turning into exaggerated and alarming rumour.
Many nations have shifted embassies out of Tokyo, and the mood grew jittery far afield from Japan, with panic-buying of iodine pills in the United States and Asian airports scanning passengers from Japan for radiation contamination.
The vast capital's usually teeming streets have been quiet, although some residents headed to work as usual. The city's neon glare is dimmed at night, in line with a power-saving drive forced by shutdowns at other atomic plants.
A moment of silence was observed at 2.46 pm on Friday, exactly one week after the earthquake struck.