Power cables have now been connected to all six nuclear reactors at Japan's tsunami-damaged Fukushima Daiichi power plant, according to operator Tokyo Electric Power.
The reconnections are the first clear sign of progress in tackling the world's worst atomic crisis in 25 years and should enable engineers to reconnect water pumps to cool fuel rods and prevent a meltdown in the reactors.
The plant was badly damaged after a 9.0-magnitude earthquake triggered a tsunami that devastated the northeast coast of Japan on 11 March.
Power was knocked out to three of the six reactors, including No 3 which contains toxic plutonium.
Tokyo Electric Power says the last two reactors to be hooked up to power from the main grid on Monday were reactors No 3 and No 4 - the two most badly damaged units.
The company says it is checking for damage to the plant's reactor cooling systems and other machinery before attempting to power them up.
It is operating equipment using grid power at reactor No 5 only, one of the least damaged reactors.
The No 5 and No 6 reactors had been shut down for maintenance when the tsunami hit.
Experts say an improvised spraying operation at the site using fire trucks may have to continue for months.
There has been little change in radiation levels at the plant after smoke was seen near the No 3 reactor, Japan's nuclear safety agency says.
Meanwhile, wind and light rain over the plant was blowing from the north-west out to the Pacific Ocean on Monday, sparing Tokyo from low levels of radiation.