The truck was to dump three tonnes of water per minute, a total 1,260 tonnes over seven hours, at the fuel storage pool on reactor No.3 at the nuclear power plant in Fukushima that was damaged by the March 11 earthquake and tsunami, which devastated the region, public broadcaster NHK reported.

Fire trucks sprayed water earlier in the day on the reactors and spent fuel pools at the plant, which is home to six nuclear reactors, to lower their temperatures. Ninety tonnes of water was sent onto reactor No.3, the Kyodo news agency said.

On Thursday, seven military fire trucks sprayed a total of 50 tonnes of water on the fuel storage pool at the reactor.

Workers should also be able to reconnect a nuclear reactor to the electrical grid Saturday to restore cooling functions at the complex 250 km north of Tokyo, the plant's operator said.