Japan began discharging contaminated water from the stricken plant earlier on Thursday in an operation it insists is safe but has generated a fierce backlash from China.

The release has also been deemed safe by the International Atomic Energy Agency (IAEA), but Beijing has banned food imports from 10 Japanese prefectures, with Hong Kong following suit.

"The ocean is the common property of all humanity, and forcibly starting the discharge of Fukushima's nuclear wastewater into the ocean is an extremely selfish and irresponsible act that ignores international public interests," Beijing's foreign ministry said in a statement.

Japan "did not prove the legitimacy" of the plan or the long-term reliability of the nuclear wastewater purification equipment", it said.

Tokyo also "did not prove the authenticity and accuracy of the nuclear wastewater data, (and) did not prove that ocean discharge is harmless to the marine environment and human health".

"What the Japanese side has done is to push the risks onto the whole world (and) pass on the pain to future generations of human beings", the statement said.

"By treating the release of the wastewater as a fait accompli, the Japanese side has simultaneously placed itself in the international dock."