South Korea's nuclear safety agency has launched an investigation into the abnormal discharge of liquid radioactive waste from a nuclear reactor to the southeast of the country.

The Nuclear Safety and Security Commission (NSSC) received a report from Korea Hydro & Nuclear Power (KHNP), the operator of nuclear power plants, at about 10:23 a.m. local time (0123 GMT) Sunday that the liquid waste of a radioactive storage tank in the Wolseong No. 2 nuclear power plant in Gyeongju, North Gyeongsang province was discharged into the ocean without going through a sample analysis.

The KHNP took measures to block leakage immediately after finding the tank outlet valve was open while preparing to release the liquid waste into the ocean, the NSSC said in a bulletin posted on its official website.

According to the KHNP's analysis of samples left in the tank, the concentration of the leaked liquid waste, estimated at about 29 tons, stood at normal levels.

The NSSC said it had dispatched experts to the power plant in a bid to investigate the exact amount and the cause of the leakage, planning to check any environmental impact by collecting seawater near the power plant.

The agency promised to announce the results of the investigation once available.