China strongly condemns the Japanese government for disregarding international opposition and starting to discharge the nuclear-contaminated water from the tsunami-wrecked Fukushima Daiichi nuclear power plant on Thursday.

China has made serious demarches to Japan and asked it to stop the discharge, a Foreign Ministry spokesperson said in a statement, adding that Japan "is bound to face international condemnation for many years to come".

The Fukushima nuclear accident, which took place 12 years ago, has already caused the leakage of large amounts of radioactive substances into the ocean, and Japan should avoid dumping nuclear-contaminated water, which could cause "a man-made secondary disaster", the spokesperson said.

The Japanese government failed to clarify a series of doubts about its ocean discharge decision, including to prove that the ocean discharge is safe and harmless to marine environment and people’s health, the spokesperson pointed out.

Also, Japan failed to have thorough consultations with other stakeholders about the ocean discharge, the spokesperson said.

"By dumping the water into the ocean, Japan... has turned itself into a saboteur of the ecological system and polluter of the global marine environment," the spokesperson said.