The emergency cooling system for reactor 1 at the Fukushima No. 1 nuclear plant may have been shut down manually before the tsunami hit March 11, according to a Tokyo Electric Power Co. spokesman and documents released by the utility.

A part of the cooling system known as the isolation condenser was down for about three hours, which could have contributed to the reactor core's meltdown.

The finding upends the government's previous conclusion that the condenser was functioning normally on March 11.