The International Atomic Energy Agency has said the situation at Japan's earthquake-damaged Fukushima nuclear plant is now reasonably stable, but warned that it could get worse.
Helicopters have been pouring tonnes of water on the facility to try and prevent a meltdown of fuel rods.
Even though the IAEA head Yukiya Amano complained about a lack of information from Japanese authorities on the crisis, his senior aide said the situation at the plant is said to be serious but 'reasonably stable'.
'It hasn't got worse, which is positive,' he said. 'The situation remains very serious but there has been no significant worsening since yesterday.'
Japanese engineers worked through the night to restore a power cable to the damaged nuclear plant.
They hope to restart pumps needed to pour cold water on overheating fuel rods and avert a catastrophe.
Even if TEPCO manages to connect the power, it is not clear the pumps will work as they may have been damaged by the natural disaster or subsequent explosions.
Repair work will stop tomorrow to allow helicopters and fire trucks to resume pouring water on the Daiichi plant, about 240km north of Tokyo.
Today, military helicopters dumped about 30 tonnes of water on two reactors at the plant.
Latest images from the plant showed severe damage, with two of the buildings a twisted mangle of steel and concrete.
'Preparatory work has so far not progressed as fast as we had hoped,' an official of plant operator Tokyo Electric Power Co (TEPCO) told a news briefing.
A cold snap is said to be hampering the effort, while work has also been slowed by the need to frequently monitor radiation levels to protect workers.
Washington and other foreign capitals have expressed growing alarm about radiation leaking from the plant, which was severely damaged by a 9.0 magnitude earthquake and tsunami a week ago.
The events of last Friday triggered a series of destructive explosions, which compromised the nuclear reactors and spent fuel storage tanks.
Many Tokyo residents stayed indoors today, however, usually busy streets were nearly deserted and many shops were closed.
Japan has also seen a substantial rise in the numbers seeking passports.
The plight of hundreds of thousands left homeless by the earthquake and tsunami worsened following a cold snap that brought heavy snow to worst-affected areas.
Supplies of water and heating oil are low at evacuation centres, where many survivors wait bundled in blankets.
About 30,000 households in the north were still without electricity in near-freezing weather, Tohuku Electric Power Co said.
The government said at least 1.6 million households lacked running water.
5,692 deaths from the quake and tsunami disaster have been confirmed, while 9,522 people are still unaccounted for in six prefectures.
