China's embassy in Japan has lashed out over Wednesday's leak of radioactive waste water from the tsunami-battered Fukushima nuclear power plant, rebuking its operator the Tokyo Electric Power Company (Tepco) and the Japanese government.

"Japan's repeated accidents in the process of treating Fukushima nuclear-contaminated water have fully exposed the chaos and disorder of Tepco's internal management," an embassy spokesman said on Thursday.

"The Japanese government's supervision measures are lacking and ineffective, which once again proves that the nuclear-contaminated water treatment equipment lacks long-term reliability."

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The spokesman added that the incident "further highlights the need for the international community to engage in supervision".

About 5,500 litres of water is estimated to have leaked from a caesium absorption tower - a section of the plant used for treating contaminated water - on Wednesday morning after a valve was left open during cleaning work.

According to Tepco, the leaked water is a mix of contaminated water from the plant's absorption system and filtered water used for cleaning. It is estimated to contain around 0.022 Terabecquerels (TBq) of radioactive substances.

Tepco said there was no risk to the public and the surrounding environment was unaffected by the leak, which was noticed by a contractor shortly before 9am local time and stopped 23 minutes later.

The utility group said that while there might be "minor contamination" to soil around the absorption tower, there was "no significant fluctuation in radiation measurements recorded at the site".

The incident was reported to the International Atomic Energy Agency (IAEA) and Japan's nuclear regulator, which is conducting an on-site investigation into the incident, it said.

China and Japan have clashed bitterly over Tokyo's decision to release 1.34 million tonnes of treated waste water over 30 years into the Pacific Ocean from the Fukushima plant, which was wrecked by an earthquake and tsunami in 2011.

Japan says the discharge - which it has continually maintained is diluted and harmless - is a necessary part of the plant's decommissioning, with storage space for the treated water running out.

The IAEA backs the release, saying it will have a "negligible effect" on the environment, and is monitoring the discharged water along with Tepco.

Beijing has been one of the fiercest critics of the operation, questioning the scientific soundness and transparency of Tepco's treatment process and accusing Japan of treating the ocean like a "sewer".

The row deepened into a full-blown geopolitical dispute, with China eventually banning all seafood imports from Japan last August.

The embassy spokesman said that China would continue to pay close attention to the impact of the incident, adding that Beijing hopes Japan "will disclose relevant information in a timely manner".

"The discharge of the Fukushima nuclear contaminated water into the sea is related to the health of all mankind, the global marine environment and international public interests," he said.

The spokesman reiterated earlier calls from Beijing for Tokyo to "face up to the concerns of its neighbouring countries and the international community".

This article originally appeared in the South China Morning Post (SCMP), the most authoritative voice reporting on China and Asia for more than a century. For more SCMP stories, please explore the SCMP app or visit the SCMP's Facebook and Twitter pages. Copyright © 2024 South China Morning Post Publishers Ltd. All rights reserved.

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