Japan's Environment Ministry is set to check radiation levels in seawater samples taken off the coast of Fukushima Prefecture. This comes after treated and diluted water began to be released from the Fukushima Daiichi nuclear power plant into the sea on Thursday.

The ministry will on Friday collect samples at 11 locations, at least one of which is about 40 kilometers from the plant's outlet of the water. A research facility will gauge the concentration of radioactive materials including tritium in each sample. The result will come out on Sunday.

The ministry has annually carried out four monitoring assessments to examine radiation levels in seawater off Fukushima. It will increase the frequency to one measurement per week and publicize the outcome on its website and social media.

Environment Minister Nishimura Akihiro said his ministry will thoroughly conduct monitoring procedures high in objectivity, transparency and credibility so as to prevent the water discharge from causing reputational damage.

The Fukushima Daiichi plant suffered a triple nuclear meltdown in the 2011 earthquake and tsunami. Water used to cool molten fuel has been mixing with rain and groundwater.

The resulting water is treated to remove most radioactive substances, but still contains tritium. Before releasing it into the sea, the plant's operator, Tokyo Electric Power Company, dilutes the treated water to reduce tritium levels to about one-seventh of the World Health Organization's guidelines for drinking water.