The cooling system in Japan’s Tokai number two nuclear plant has broken down.
The latest crisis comes as authorities struggle to avoid a possible meltdown in two of the reactors at the Fukushima Daichi plant damaged in Friday’s devastating earthquake.
Thousands of people there are being scanned for possible radiation exposure after being evacuated from their homes.
Experts say the health risk from quake-hit reactors is low, with winds likely to carry any contamination out to the Pacific Ocean.
Seawater is reportedly being pumped into reactors 2 and 3 at the Fukushima plant in an attempt to cool them down.
The Tokai plant lies further to the south. A state of emergency has also been declared at Onagawa, although the authorities say it’s under control.
It was on Saturday that an explosion occurred at number 1 reactor in Fukushima, blowing off the roof.
The government has admitted a second explosion at the plant is possible, but says a meltdown is unlikely.