International Atomic Energy Agency (IAEA) Director-General Rafael Grossi conducted two hours of inspections at Fukushima Daiichi nuclear power plant on Thursday morning.

He looked over tanks containing treated water, as well as the plant's liquid processing system.

A March 11, 2011, undersea earthquake off Japan's east coast triggered a massive tsunami that overwhelmed cooling systems at several of the Fukushima Daiichi plant's reactors and caused the worst nuclear accident since Chernobyl.

Decommissioning is expected to take around four decades, with painstaking work to remove molten fuel from damaged reactors among the tasks ahead.

A more immediate challenge involves disposing of more than a million tonnes of treated water from the site that is currently stored in massive tanks.

Japan's government has endorsed a plan to release the water into the ocean after treating it to remove almost all radionuclides and diluting it.

The process will take place over many years, and has been backed by the IAEA and, this week, Japan's Nuclear Regulation Authority.

In a video message tweeted by Grossi from Fukushima, he insisted the release would "be done in full conformity with the international standards and therefore it will not cause any harm to the environment."

But the plan has worried local fishing communities concerned about the reputation of their catch and prompted criticism from China and South Korea.

(With inputs from AFP)

(Cover: IAEA Director-General Rafael Grossi inspects Fukushima Daiichi nuclear power plant in Okuma, Fukushima prefecture, May 19, 2022. /CFP)