Engineers have restored power to the control rooms of five of the six reactor units of the Fukushima nuclear electricity station.
Efforts to re-launch the cooling systems are being hampered by abnormally high radioactivity in water flooding the turbine halls.
At Unit 3, the water is one and a half metres deep and radioactive at 10 thousand times the normal level.
Emergency teams have to pump more and more fresh water in order to avert overheating in the damaged reactors.