Tokyo (CNN) -- Another reactor at Japan's Fukushima Daiichi nuclear plant lost its cooling capabilities Monday, a government official said.
The problem was detected in the plant's No. 2 reactor Monday afternoon after an explosion rocked the building containing the plant's No. 3 reactor, Chief Cabinet Secretary Yukio Edano told reporters.
"We think that the hydrogen explosion in (the building housing) reactor No. 3 caused the cooling system of reactor No. 2 to stop working," Edano said.
Water levels were falling and pressure was building up inside the No. 2 reactor, he said, and officials were working on a plan to release gas and also inject seawater into that reactor.
Workers have been injecting seawater in a last-ditch effort to cool down fuel rods and prevent a full meltdown at two other reactors at the plant -- No. 1 and No. 3 -- after an 8.9-magnitude earthquake and ensuing tsunami Friday knocked out the reactors' cooling systems.
Japanese officials have said that they are operating under the presumption that there may be a partial meltdown in the No. 3 and No. 1 nuclear reactors. Authorities have not yet been able to confirm a meltdown, because it is too hot inside the affected reactors to check.
Fukushima, Japan - Nuclear Reactor Explosion