The head of the U.N.'s nuclear energy agency says Japan is racing against the clock to cool the overheating nuclear reactors at its crippled power plant.
International Atomic Energy Agency head Yukiya Amano gave the critical assessment after flying into Tokyo on Friday and being briefed by Japanese Prime Minister Naoto Kan.
Amano says he underscored his concern about the extreme seriousness of the accident at the Fukushima Dai-ichi nuclear plant.
A week after the earthquake and tsunami damaged the plant, authorities are still trying to reconnect a power supply to restart cooling systems. One reactor, Unit 3, is drawing urgent concern, with its nuclear fuel storage pool dangerously low of water, exposing the stored fuel rods.