Japan's national fisheries federation reiterated its continued opposition to the government's planned release of Fukushima nuclear-contaminated wastewater into the ocean on Monday during a meeting with Prime Minister Fumio Kishida.

Masanobu Sakamoto, head of Japan's National Federation of Fisheries Cooperative Associations, said the group continued to oppose the ocean release project, which would erode the reputation of seafood from Fukushima and nearby areas.

NHK reported on Monday that Japan plans to release Fukushima nuclear-contaminated water into the ocean as early as Thursday. But the media outlet didn't cite a source for the information.

Kishida had earlier said that his cabinet would meet on Tuesday to formally determine the start of the release.

Acquiring approval from the fishery industry is a crucial factor for the Japanese government and the Tokyo Electric Power Company (TEPCO), the operator of the Fukushima Daiichi nuclear power plant operator. They have pledged not to go ahead with the ocean release without the consent of the fishermen, but no decision has yet been made regarding what to do with that promise.

During his visit to the Fukushima nuclear plant on Sunday, Kishida urged the operator, Tokyo Electric Power Company Holdings Inc, to ensure the safety of the water release.

Once the date for release is determined, the nuclear-contaminated wastewater, equivalent to the contents of 500 Olympic-size swimming pools, will be released into the ocean.

The predicted decades-long release raised anxiety among the fishing industry, which was "gravely concerned," Sakamoto said.

Kishida acknowledged the concerns but said the water release had become a pressing matter, and asked the fishermen to understand that the disposal of the water was necessary.

"I promise that we will take on the entire responsibility of ensuring the fishing industry can continue to make their living, even if that will take decades," he said.

An opinion poll showed on Sunday that the disapproval rate of the Japanese government headed by Kishida has reached 50 percent for the first time since last December, with a total of 88.1 percent surveyed expressing concerns over dumping radioactive wastewater into the ocean.

(With input from agencies)