Protesters gather on Tuesday outside the prime minister's office in Tokyo during a rally against the Japanese government's plan to release radioactive water into the Pacific Ocean. KAZUHIRO NOGI/AFP

Japan announced on Tuesday that it will start releasing nuclear-contaminated water from the destroyed Fukushima Daiichi Nuclear Power Plant into the Pacific Ocean as early as Thursday, a move that sparked widespread criticism from the international community and local residents.

China voiced strong opposition after the announcement, saying that the act is "extremely selfish and irresponsible". It strongly urged the Japanese government to reverse its wrong decision.

On Tuesday, Vice-Foreign Minister Sun Weidong summoned Japanese Ambassador to China Hideo Tarumi and lodged solemn representations over the decision.

Sun said that Japan's move disregards the strong concerns and firm opposition of the international community.

Condemning the decision as "extremely selfish and irresponsible", Sun said that Japan is putting its own interests above the long-term well-being of the entire humanity. "China is gravely concerned and strongly opposed to this," he said.

If Japan insists on the discharges, China will take all steps necessary to protect the ocean, ensure food safety and safeguard people's life and health, he added.

Japanese Prime Minister Fumio Kishida gave the final go-ahead to the radioactive water discharge plan on Tuesday and said the government will oversee the release of "treated water", which he called "essential" for the safe decommissioning of the Fukushima plant.

Kishida said that authorities will address the concerns of local communities and fishermen over reputational damage and continuation of business, but his assurances have failed to ease doubts among Japan's people.

As the Kishida Cabinet cleared the plan, people from across the country staged a protest outside the prime minister's office on Tuesday.

Shigeru Tokiwa, a book editor in Tokyo who joined the protest, said: "This administration has been lying from the very beginning. It is just shameful, isn't it?"

Naomi Hori, a tour guide from Chiba Prefecture, said: "Nobody is convinced about the safety of the plan. The Japanese government and Tokyo Electric Power Co (the operator of the plant) are just piling up lies. Basically, no one is taking responsibility."

A massive earthquake and tsunami on March 11, 2011, destroyed the Fukushima plant's cooling systems, causing three of its reactors to melt and contaminate their cooling waters.

Sei Tamamori, a resident of Kawasaki, Kanagawa Prefecture, said, "The government calls the water 'treated', but it is actually contaminated water that the government is trying to rebrand."

At a regular news briefing on Tuesday in Beijing, Foreign Ministry spokesman Wang Wenbin said that the legitimacy and safety of Japan's ocean discharge plan have been questioned over and over again for the past two years.

China strongly urges Japan to rectify its wrong decision, revoke the ocean discharge plan, communicate with neighboring countries with sincerity and goodwill, dispose of the contaminated water in a responsible manner and accept rigorous international oversight, he added.

On Tuesday, John Lee Ka-chiu, chief executive of China's Hong Kong Special Administrative Region, announced an immediate ban on importing Japanese food products.

The Macao Special Administrative Region has also announced a ban on the import of live and fresh food products from 10 prefectures and regions of Japan. The ban will take effect on Thursday.

Xi Tianqi and Prime Sarmiento in Hong Kong contributed to this story.