Japanese Prime Minister Naoto Kan on Friday called the country's ongoing fight to stabilise the stricken Fukushima nuclear plant "very grave and serious", after officials announced a suspected breach in one of the reactors.
A breach would raise the possibility of more severe radioactive contamination, two weeks after a devastating earthquake and tsunami disabled the nuclear complex.
"The situation today at the Fukushima Dai-Ichi power plant is still very grave and serious. We must remain vigilant," Mr Kan said. "We are not in a position where we can be optimistic. We must treat every development with the utmost care."
The apparent breach is in Unit 3 and it might be a crack or a hole in the stainless steel chamber of the reactor core or in the spent fuel pool that's lined with several feet of reinforced concrete.
The Nuclear and Industrial Safety Agency said suspicions were raised when two workers suffered skin burns after wading into water 10,000 times more radioactive than levels normally found in water in or around a reactor.
People who reside in the immediate area have been told to stay inside or vacate the area.