Japan's nuclear regulator has authorized a plan to release treated water from the crippled Fukushima Daiichi nuclear power plant into the ocean.

The Nuclear Regulation Authority held an extraordinary meeting on Friday during which it discussed and gave final approval of the plan drawn up by the plant's operator, Tokyo Electric Power Company, in line with a government decision.

Reactors at the Fukushima Daiichi plant suffered meltdowns in the March 2011 earthquake and tsunami disaster.

Water used to cool molten fuel mixes with rain and groundwater. The accumulating water is treated to remove most of the radioactive materials and stored in tanks on the plant's premises.

The filtered water still contains tritium. The government plans to dilute the water so that its tritium level falls below national regulations and start releasing it from around next spring.

The nuclear regulator approved the plan drafted by TEPCO in May and invited opinions from the public.

NRA officials received a report from its secretariat on the public opinions during their Friday meeting. Of the 1,233 responses, 670 were about technical matters such as the measurement of the concentration of tritium in the treated water and the plant's ability to withstand earthquakes.

The officials discussed the opinions and concluded that what TEPCO has done so far with the treated water and its plan are reasonable.

The regulator says that going forward, it will check whether the operator is making preparations as scheduled.

TEPCO began work last December on construction of an undersea tunnel to be used for the release of treated water.

It also plans to build a facility to dilute treated water after winning agreement from Fukushima Prefecture and the plant's host municipalities. The utility hopes all the construction work will be completed around mid-April in 2023.

But concerns persist among locals, including fishers, about potential reputational damage for products from the region.