Japanese authorities are hoping a new power line could restore cooling systems at the Fukushima nuclear power plant, which was struck by last week's huge earthquake and tsunami causing dangerous surges in radiation levels and prompting fears of a meltdown.

Work is nearing completion on the power line which the plant's operator, Tokyo Electric company, hopes will revive electric-powered pumps, allowing a steady cooling water supply to reactors and spent fuel storage ponds.

Four out of the six reactors in the nuclear power plant have been damaged and officials say the No.3 reactor was the top priority because it had the highest radiation levels following an explosion at the building it is housed in on Monday. Sea water has been pumped into the reactor to prevent overheating.

Attempts by a military helicopter to drop water on the reactor failed on Wednesday according to local media reports.

The Japan nuclear agency had said earlier in the day that the injection of sea water was proceeding smoothly. Cooling systems have failed so far at reactor numbers 1,2 and 4.