A fire extinguisher system has broken down at a nuclear power plant in northern Japan due to a record cold weather.
Hokkaido Electric Power Company says a worker discovered the problem at its Tomari nuclear plant in the country's northernmost prefecture of Hokkaido early Saturday morning.
The problem affected equipment designed to maintain water pressure in the event of firefighting at the No.1 and No.2 reactors. All three of the plant's reactors have been offline since 2012, following the Fukushima nuclear accident.
The utility says a part of the equipment was frozen due to the severe cold, causing the system to break down. It says there is no problem with the plant's fire extinguisher system, and the problem did not affect firefighting functions.
Temperatures fell to minus 30 degrees Celsius or lower in many parts of the prefecture on Saturday. A nearby town recorded minus 12.7 degrees Celsius.
The company also says the temperature was nearly minus five degrees in the room which houses the equipment, but a worker forgot to turn on the heating system.
The utility says it will work quickly to restore the faulty equipment and take measures to prevent a recurrence.