The operator of the Fukushima Daini Nuclear Power Plant, a facility currently being decommissioned, said Sunday it suspended cooling of a spent fuel pool after a pump malfunction triggered an alert.

Tokyo Electric Power Company Holdings (TEPCO) said an alarm for the spent fuel pool of the plant's No. 1 reactor went off at around 2:45 p.m. local time on Sunday. Workers shut down the pump after smoke was detected at the site, halting the pool's cooling system.

Radiation levels around the nuclear plant have shown no change, and no injuries have been reported so far, TEPCO said, adding that it was investigating the cause of the malfunction and working to repair the pump as quickly as possible to restore cooling.

According to public broadcaster NHK, the pool water temperature stood at 26.5 degrees Celsius when the cooling system was halted, leaving about eight days before it would exceed the 65-degree Celsius threshold set for safe operation.

The four-reactor Fukushima Daini plant sits about 12 km south of the Fukushima Daiichi plant, both of which were crippled by a massive earthquake and an ensuing tsunami in March 2011, prompting TEPCO to decommission both facilities.