Japan has summoned China’s ambassador after businesses were inundated by ‘harassment’ phone calls following the release of water from the Fukushima nuclear power plant, with the country’s Prime Minister Fumio Kishida saying stones were thrown at its diplomatic missions and schools in China.

“There have been numerous harassment calls believed to originate from China and instances of stones being thrown into the Japanese embassy and Japanese schools. It must be said these are regrettable,” Fumio Kishida told reporters 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,” he said.

Last week, China banned all seafood imports from its neighbour after Japan began releasing cooling water from the stricken Fukushima plant in an operation that Tokyo and the UN’s nuclear watchdog have said is safe.

Since then, randomly chosen Japanese businesses ranging from bakeries to aquariums have reportedly received thousands of sometimes abusive crank calls believed to be from Chinese numbers.

Social media users in China have posted recordings and videos of these calls, some of which have attracted tens of thousands of likes and a large number of comments.

Japan’s embassy over the weekend urged the tens of thousands of Japanese living in China to keep a low profile and not talk loudly in public.

Deputy Foreign Minister Masataka Okano told Chinese ambassador Wu Jianghao that Beijing 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 earlier said in a statement.

“Since the start of the discharge… there have been numerous phone calls and other harassment regarding the discharge that are suspected of originating from China. The situation has not improved since then,” Okano told Wu.

“A number of similar incidents are also happening in China against Japan-related facilities. This is extremely regrettable and we are deeply concerned,” he said, according to the release.

On Monday, it said it had increased security measures outside Japanese schools and diplomatic missions in China.

A spokesperson for China’s foreign ministry said it was not aware of the matter when asked about the harassment accusations at a regular briefing on Monday.

According to Japanese media, there have been several incidents of stones and eggs being thrown at Japanese schools.

In China, a rock was thrown at a Japanese school in the coastal city of Qingdao on Thursday, according to the consulate-general of Japan in the city.

When asked about the incident in Qingdao and the harassment calls, Chinese foreign ministry spokesperson Wang Wenbin defended China’s record of keeping foreigners safe.

“China always safeguards the safety and lawful rights and interests of foreign nationals in China in accordance with law,” Wang said.

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

Plant operator TEPCO says that all radioactive elements have been filtered out except for tritium, levels of which are within safe limits.

Test results since the start of the discharge have confirmed this, according to Japanese authorities.