The operator of Japan's crippled Fukushima Daiichi nuclear power plant is planning to start releasing treated and diluted water from the facility into the ocean on Thursday afternoon, if preset scientific and safety criteria are satisfied.

On Tuesday, the Japanese government decided to authorize the start of release as early as Thursday.

The plant run by the Tokyo Electric Power Company suffered a triple meltdown in the wake of the 2011 earthquake and tsunami. Since then, rain and groundwater have mixed with the water used to cool molten fuel at the plant. The accumulated water is treated to remove most radioactive material, but still contains tritium.

The government aims to dilute the treated water to reduce tritium levels to about one-seventh of the level stated in the World Health Organization's guidelines for drinking water quality.

TEPCO on Tuesday night filled the "discharge vertical shaft" with the treated and diluted water and is now measuring the tritium concentration of the water to confirm if it is diluted as targeted.

TEPCO says the result is expected to be available on Thursday morning, and the release may start at around 1 p.m. if there are no problems with the result and weather conditions.

After the release is set in motion, the water will be mixed with more seawater before flowing out from the shaft. The water will then move to a tunnel under the seabed and come out from the outlet one kilometer off the coast.

TEPCO says it plans to carry out the first round of release over 17 days to discharge 7,800 tons of treated water. The company plans to release 31,200 tons of treated water in the current fiscal year through March. The quantity is equivalent to the volume of about 30 storage tanks.