Attempts to cool down a stricken reactor at the Fukushima Daiichi nuclear plant suffered an early setback on Thursday after seawater dumped from the air failed to bring down radiation levels.
Radiation readings taken 20 minutes after self-defence force helicopters doused the plant's No 3 reactor remained unchanged, Tokyo Electric Power said, according to Kyodo news agcncy.
The use of Japanese military helicopters to drop seawater onto the plant's reactor marked the opening of a new front in the battle to avert nuclear meltdown, according to The Guardian.
The crews, using CH-47 Chinook helicopters, worked in 40-minute shifts to limit their exposure. However, strong winds appeared to blow much of the water from the target, limiting the dangerous operation's effectiveness.
Dozens of people have remained at the scene, working against the clock to prevent harmful levels of radioactive material from spewing into the air.
Officials had initially ruled out using helicopters, saying the radiation would be too dangerous, CTV.ca reports.