The fuel rods at one of the quake-stricken nuclear reactors in north-eastern Japan were dry late Monday, as the levels of cooling water fell despite emergency efforts, DPA reported.
Authorities had been trying to keep the core of reactor 2 at the Fukushima I plant cool with sea water after Friday's magnitude-9 earthquake and tsunami cut the power to the normal cooling systems.
Fears were increasing that temperatures in the core could rise to a level where the rods could melt their way through the core's steel walls, an event known as a meltdown.
If the containment structure around the core has been cracked by the quake, a meltdown could cause radiation to leak into the surrounding environment.