The planned, decades-long discharge of accumulated water from the devastated nuclear facility has been approved by the International Atomic Energy Agency (IAEA) as meeting global standards.

Its chief Rafael Grossi, at a meeting in Iwaki, Fukushima prefecture, acknowledged however that concerns remains.

"All these complex graphs and statistics are one thing but the reality, the reality of people, the reality of the economy, the reality of the social mood and perceptions may be different," he told a meeting of local residents and officials.

Some 1.33 million cubic metres of groundwater, rainwater and water used for cooling has accumulated at the Fukushima site, which is being decommissioned after several reactors went into meltdown following the 2011 tsunami which badly damaged the plant.

Plant operator TEPCO treats the water through its ALPS processing system to remove almost all radioactive elements except tritium, and plans to dilute it before discharging it into the ocean over several decades.

The plan is opposed by some regional neighbours, with Beijing vocally condemning the plan, as well as some in Fukushima, particularly fishing communities who fear customers will shun their catches.

Grossi said the IAEA was not involved in the process to "give cover... to decorate something that is bad."

"When it comes to this activity here, what is happening is not some exception, some strange plan that has been devised only to be applied here and sold to you," he added.

"This is, as certified by the IAEA, the general practice that is agreed by and observed by many, many places, all over the world."

Still, there is palpable anger among some local residents who fear the reputational damage of the release.

Tetsu Nozaki, chairman of the Fukushima Prefectural Federation of Fisheries Co-operative Associations, argued Japan's government was misrepresenting local sentiment, which he said remained strongly opposed to the plan.

"We fishery operators are left with no choice but to react emotionally and harden our attitude," he told Grossi.

"I beg you to realise... that this project of the release of ALPS-processed water is moving ahead in the face of opposition."

Grossi said he had no "magic wand" that could assuage concerns but pointed out the IAEA will set up a permanent office to review the release over decades.

"We are going to stay here with you for decades to come, until the last drop of the water which is accumulated around the reactor has been safely discharged," he said.

Grossi is due to visit the Fukushima plant later Wednesday, and will make stops in regional neighbours including South Korea after his Japan trip.