The operator of the Fukushima Daiichi nuclear plant says an alarm that monitors tanks storing radioactive wastewater was turned on mute.

Tokyo Electric found the monitoring computer's alarm sound was turned off, after they investigated two tanks, which showed a decrease in water level.

Due to continuous leaks at the crippled plant, Tepco monitors these tanks with a water level indicator.

Workers investigated after finding the indicator showing a change in water levels, but determined the indicator was mistaken.

They then realized the alarm sound to indicate leaks at Fukushima Daiichi was turned off.

This means that until April 8th, the alarm would not have been noticed if leaks had occurred in any of the 433 tanks.

Tepco is now trying to find out when the alarm sound was set to mute.