Japan has raised concerns to the Chinese government following abusive calls received by businesses and institutions in Japan from numbers with Chinese dialing codes about the release of contaminated water from the damaged Fukushima plant.
It comes as Tokyo said seawater around the nuclear plant is showing no detectable levels of radioactivity.
The calls had begun since the release of contaminated water from Fukushima, and have been made to government departments, schools and even an aquarium.
The callers speak in Chinese, Japanese and English - and sometimes use abusive language speaking about their opposition to Japan's decision to release the treated nuclear water.
China has described the discharge as an "extremely selfish and irresponsible act" and has put a ban on importing seafood from Japan.
Meanwhile, Tokyo is hoping regular radiation testing in the waters near the plant will allay concerns from neighbouring countries and fishing groups.
Weekly test results will be published for the next three months.
More than a million tonnes of water stored at the nuclear plant will be discharged over the next 30 years.
