An operator of waste incineration plants in Tokyo says it has found a high density of radioactive materials in ash at one of its plants.

An Edogawa ward plant, which handles general household garbage, detected 9,740 becquerels of radioactive materials per kilogram of ash.

The ash was collected from a device to filter exhaust fumes.

The plant's operator, an organization jointly set up by Tokyo's 23 wards, believes that radioactive cesium built up through the incinerating process.