Japan's prime minister ate what he called "safe and delicious" fish from Fukushima on Wednesday, days after wastewater was released from the area's crippled nuclear plant into the Pacific.

A video clip showing Fumio Kishida eating Fukushima fish, published on social media by his office, comes after China banned all seafood imports from its neighbour following the discharge that began on August 24.

"This is very good," Kishida said as he chewed on a slice of flounder sashimi, calling on viewers to enjoy "safe and delicious" Japanese seafood to support the northeastern region.

The clip, overlaid by cheery music, showed the conservative leader joined by three other ministers at his office for sashimi, boiled pork, fruits, rice and vegetables from the Fukushima region.

It was designed to promote products from the area 12 years after Fukushima was devastated by a huge earthquake and tsunami that triggered one of the world's worst nuclear disasters.

Even before the wastewater release, many in Japan's fishing industry were worried about what it would do to the reputation of the country's seafood domestically and abroad.

The discharge, equivalent to more than 500 Olympic swimming pools, is expected to take decades and will allow engineers to start removing highly dangerous radioactive fuel from three wrecked reactors.

Bricks and eggs have been thrown at Japanese schools and consulates in China and Tokyo has advised its nationals there to keep a low profile. Businesses in Japan have also been swamped with nuisance calls from Chinese numbers.

Kishida was expected to visit Tokyo's main Toyosu fish market on Thursday to sample more Fukushima fish.

Japan has demanded that China -- its biggest market for fish -- drop its ban on seafood imports while warning it will complain to the World Trade Organization (WTO).

Kishida's government is also reportedly planning a package of financial aid for the fishing industry while also helping it find new export markets.

Rafael Grossi, the head of the International Atomic Energy Agency (IAEA), reiterated on Wednesday that the water being released was safe according to the UN watchdog.

In a show of support for Japan, the US ambassador to Japan, Rahm Emanuel, was due to visit the Fukushima area on Thursday and eat locally caught seafood.