The nuclear plant, which houses six reactors, was damaged by Friday's 9-magnitude earthquake and subsequent tsunami, which took out cooling systems.
Workers attacked the situation from the air and from the ground Thursday, the Los Angeles Times reported. Helicopters made four passes, dumping seawater, and water was also sprayed first from police water cannons and then from military trucks normally used for riot control.
Kyodo reported 64 tons of water was dumped on the plant to try to cool down spent fuel rods from the No. 3 and No. 4 reactors but failed to lessen radiation levels immediately.
Smoke later was spotted coming from the No. 2 reactor, indicating water in its cooling pond was boiling as well, Kyodo said.
Tokyo Electric Power Co. said electricity to power the cooling systems would not be restored until at least Friday, a day later than officials had hoped. Three of the six reactors were damaged by hydrogen explosions.
Three of the plant's reactors were shut down for a routine check prior to Friday's disaster.
CNN reported the utility increased the number of workers at the site Wednesday from 50 to 180.
The hydrogen and other blasts have destroyed the buildings housing the reactors at No. 1, No. 3 and No. 4, and damaged the containment vessel's pressure-suppression chamber at the No. 2 reactor.
TEPCO has said an estimated 70 percent of the nuclear fuel rods have been damaged at the No. 1 reactor and 33 percent at the No. 2 reactor. The city of Tokyo was spared a major power failure Thursday as frigid temperatures overloaded a stressed electrical system, officials said. The system almost reached its limit Thursday morning, Kyodo News reported. Tokyo Electric Power Co. said demand was 33.3 million kilowatts, within 200,000 kilowatts of capacity.
Many companies sent workers home early. Rail services were asked to cut the number of trains running Thursday evening. Tokyo Electric had already planned rolling blackouts in the capital region.
U.S. President Barack Obama Thursday pledged U.S. aid. He said he told Japanese Prime Minister Naoto Kan, "the Japanese people are not alone in this time of great trial and sorrow."
America would lend a helping hand to its longtime ally with whom it shares "the ties of family, the ties of culture and the ties of commerce."
"Above all, I am confident that Japan will recover and rebuild because of the strength and spirit of the Japanese people," Obama said.