TOKYO: Japan threatened on Tuesday to take China to the World Trade Organization (WTO) to seek a reversal of Beijing's ban on all of its seafood imports after the release of treated radioactive water from the stricken Fukushima Daiichi nuclear power plant.

Foreign Minister Yoshimasa Hayashi told reporters that Japan would take "necessary action (on China's aquatic product ban) under various routes including the WTO framework".

Filing a WTO complaint might become an option if protesting to China through diplomatic routes is ineffective, Economic Security Minister Sanae Takaichi said separately.

The comments came as Japanese businesses and public facilities continued to receive harassment calls from phone numbers with the +86 Chinese country code, with many reporting callers complaining of the Fukushima water release.

Fukushima prefectural government and public facilities in the prefecture have received about 3,000 such calls, Kyoto News reported, quoting the prefecture governor.

The power plant operator Tokyo Electric Power has received about 6,000 such calls to date, local media reported, and the government said it was seeking help from telecommunications companies to block the calls.

An increasing number of landline phone users are requesting to block foreign numbers, said a spokesperson at NTT Communications, a Nippon Telegraph and Telephone unit. NTT and other phone companies including KDDI and SoftBank Corp are discussing measures following the government's request.

NTT East, which serves the eastern half of the country including Fukushima, said it had set up a customer service centre on Tuesday specifically for harassment calls from overseas, in response to the government's plea.

"It is extremely regrettable and concerning about the large number of harassment calls that have likely come from China," Trade Minister Yasutoshi Nishimura said during a news conference. He said that according to the people of Fukushima some calls were even going to hospitals.

"Human life is at stake now. Please stop the calls immediately," Nishimura said.

The minister said the government was gathering information on the reports of movements to boycott Japanese products in China and would work with business leaders to address the situation.

Japan is also conducting interviews with local travel agencies to gather information about the status of travel to Japan from China after media reports that some Japan-bound tours have been cancelled.

"Some travel agencies responded that they had received cancellation requests while others said they had received inquiries about the safety of food and beverages, and the possibility of postponing or cancelling tours," Japan's Land Minister Tetsuo Saito told reporters.

The move came after China earlier this month lifted pandemic-era restrictions on group tours for Japan and other key markets.