Workers at the stricken Japanese nuclear power plant on Sunday reported a spike in radiation readings, indicating a possible new leak.
Readings of up to 1,800 millisieverts per hour and radioactive strontium were detected near the reactors and a connecting pipe carrying cooling water, the operator Tokyo Electric Power Company (TEPCO) said.
Exposure to such levels would give an adult a fatal dose of radiation within four hours.
But the water level inside the cooling tanks had not fallen, TEPCO said, indicating that it was not clear that the radioactive water came from a leak.