Japan's Environment Ministry says dozens of bags containing radioactive soil were swept into rivers following a powerful typhoon last month. The dangerous waste was produced as a result of the 2011 nuclear disaster.
The waste has been stockpiled at temporary storage sites in Fukushima and neighboring prefectures.
Officials say they have confirmed that 90 bags in Fukushima and one in Tochigi Prefecture were swept away by Typhoon Hagibis after inspecting all the storage sites.
They say at least 25 of the bags were found empty, meaning that the tainted soil was carried away in floodwaters.
But the officials add that radiation levels around the sites remain unchanged.
They plan to install barriers around the storage sites to prevent further such incidents in addition to looking into what caused the problem.