"We find this very regrettable and feel extremely worried," an embassy press officer told AFP.

They urged Beijing to "ensure the safety of these embassies and consulates in China in accordance with international law, including some facilities related to Japan, and including Japanese people."

Asked by AFP about reports that Chinese people had thrown bricks at Tokyo's embassy in Beijing and made harassing phone calls, the press officer confirmed they were true.

"Some individuals have come to our (embassy) entrance," they said.

"They took these kinds of actions then were led away by armed police," they explained.

"Harassing calls are answered every day, especially on weekends, beginning last Thursday and Friday, delaying our normal work," they added.

Last week, China banned all seafood imports from its neighbour as Japan began releasing cooling water from the crippled Fukushima plant in an operation that Tokyo and the United Nations' nuclear watchdog have said is safe.

Since then, Japan has urged its citizens in China to keep a low profile and has increased security around schools and diplomatic missions. Businesses in Japan, meanwhile, have been swamped with nuisance calls from Chinese numbers.

Japanese Prime Minister Fumio Kishida on Monday urged China to ensure its people "act in a calm and responsible manner".