"TEPCO has confirmed that there was no significant fluctuation in radiation measurements recorded at the site. The event does not pose any risk to the public and there is no environmental impact off-site," the IAEA said in a statement published on Wednesday.
The statement also said that the leaked water was from the system filtering water "as part of the ongoing decommissioning activities at the site."
"The event is not related to the discharge of the Advanced Liquid Processing System (ALPS) treated water," it added.
The International Atomic Energy Agency remains in contact with authorities in Japan, according to the statement.
The leak was detected by a station employee at 9 a.m. local time (00:00 GMT) on Wednesday during the inspection of the equipment. The employee found that 10 of the 16 valves of the station that should have been closed, were open.
TEPCO estimated that the volume of water stood at 5.5 tonnes and contained radionuclides, including radioactive cesium and strontium. The content of radioactive substances is estimated at 22 billion Becquerels. A significant part of the water has been presumably absorbed into the soil. A monitoring point installed next to a nearby sewage channel does not show radiation levels changes. Japanese Parliamentary Vice-Minister of Economy, Trade and Industry Nobuhiro Yoshida apologized for the leak.
China has called on Japan to facilitate the establishment of an international monitoring mechanism after a leak of contaminated water occurred at Japan's Fukushima nuclear power plant, the Chinese Embassy in Tokyo said on Thursday.
"Ineffective control measures by the Japanese government again prove that radioactive water treatment equipment is unreliable in the long term, which once again stresses the necessity of an international supervision," the Chinese embassy said in a statement.
Beijing has also pointed to continuous incidents related to the water release from the nuclear power station, saying that they demonstrate "chaos and disorder" in the internal operation of TEPCO, the statement read.
"The discharge of contaminated water from the Fukushima-1 nuclear power plant into the sea concerns the health of all humankind, the global marine environment and international public interests. We again insist that Japan should attach due importance to the concerns of neighboring countries and the international community," the statement said.
Beijing has urged Tokyo to hold consultations with all parties involved, promote the establishment of an "effective international monitoring mechanism" engaging the stakeholders, and dispose of radioactive water in "a scientific, safe and transparent manner," the statement added.
Japan started releasing part of the estimated 1.34 million tonnes of Fukushima treated water into the ocean in August 2023. The entire process is expected to take at least 30 years. The International Atomic Energy Agency said that treated wastewater would have a negligible radiological impact on the marine environment and human health. However, China has banned all seafood from Japan over concerns about radioactive contamination.