TOKYO, Japan - Japan's prime minister urged China to ensure its people "act in a calm and responsible manner" after instances of stones being thrown at diplomatic missions and schools, following the release of wastewater from the Fukushima nuclear plant.

"There have been numerous harassment calls believed to originate from China and instances of stones being thrown at the Japanese embassy and Japanese schools. It must be said these are regrettable," Prime Minister Fumio Kishida said on Monday.

"We summoned the Chinese ambassador to Japan today and strongly urged him to call on Chinese people to act in a calm and responsible manner," Kishida told reporters.

Japan's Deputy Foreign Minister Masataka Okano told the ambassador, Wu Jianghao, that China should properly inform the public "rather than unnecessarily raising people's concerns by providing information that is not based on scientific evidence", the foreign ministry said in a statement.

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Asked what action Beijing would take over the stone throwing, Beijing's foreign ministry spokesman Wang Wenbin said on Monday that China "always protects the safety and legitimate rights and interests of foreigners in China, in accordance with law".

"We strongly urge the Japanese side to face up to the legitimate concerns of all parties, immediately stop the discharge of nuclear-contaminated water into the sea, fully consult with its neighbours and other stakeholders, and earnestly dispose of nuclear-contaminated water in a responsible manner," Wang told a regular briefing.

On Sunday, Japan's foreign ministry urged its citizens in to China to be "cautious in your speech and behaviour. Do not speak Japanese unnecessarily or too loudly".

"If you need to visit a Japanese embassy, consulate general, or Japanese school, pay close attention to your surroundings," it added.

"If you happen to come across a protest or other such activities, do not approach them and do not take pictures of them with your smartphones."

A range of businesses in Japan, from bakeries to an aquarium, have reportedly been subjected to thousands of crank calls that have included abusive and racist language.

Social media users in China have posted recordings and videos of the calls, some of which have attracted tens of thousands of likes.

- 'Scientifically justified process' -

Japan began releasing more than 500 Olympic swimming pools' worth of diluted wastewater from Fukushima into the Pacific on Thursday, 12 years after a tsunami knocked out three reactors in one of the world's worst atomic accidents.

All radioactive elements have been filtered out except for tritium, levels of which are within safe limits and below that released by nuclear power stations in their normal operations -- including in China, plant operator TEPCO says.

Test results from seawater and fish samples near the plant since the start of the discharge -- which will take decades to complete -- have confirmed this, according to Japanese authorities.

"Even after the ocean release, the United States, for example, expressed its position that it is satisfied with Japan's safe, highly transparent and scientifically justified process," Kishida said Monday.

"We would like to convey these voices from the international community to the Chinese government."

US Ambassador to Japan Rahm Emanuel plans to visit Fukushima this week and publicly eat locally caught fish in a show of support to Japan, according to media reports.