Staff had been evacuated after radiation levels spiked for a second time to their highest levels so far at Reactor 3 and a second fire broke out at Reactor 4.
Shortly after the evacuation, a military helicopter was seen carrying water to the plant, apparently to cool down the most troubled reactors, according to Japan's NHK public broadcaster.
The flames at the fourth reactor's containment vessel were brought under control but white smoke or steam was seen rising from the facility in the northeast of the earthquake and tsunami-devastated country.
Officials have been struggling to address the failure of safety systems at several of the plant's reactors. Read More