The number one and three reactors at the same plant have experienced the same problem, followed by explosions in the buildings surrounding those reactors in the wake of Friday's 8.9-magnitude quake and devastating tsunami.

The number two reactor has totally lost its cooling function, public broadcaster NHK said, citing the country's Nuclear and Industry Safety Agency.

Officials at TEPCO were not immediately available to comment.

The plant is located 250 kilometres (120 miles) north of Tokyo.