The former executives had in 2022 been ordered to pay 13.3 trillion yen in a suit brought by shareholders over the nuclear disaster triggered by a massive tsunami in 2011.

Shareholders had argued the catastrophe could have been prevented if Tokyo Electric Power Company (TEPCO) bosses had listened to research and implemented preventative measures like placing an emergency power source on higher ground.

But the defendants countered that the risks were unpredictable, and the studies cited were not credible.

The court did not immediately confirm Friday's news reports when contacted by AFP.

The 13.3 trillion yen damages award was believed to be the largest amount ever ordered in a civil suit in Japan.

It was meant to cover TEPCO's costs for dismantling reactors, compensating affected residents, and cleaning up contamination.

In 2015, British oil giant BP was ordered to pay $20.8 billion for the Gulf of Mexico oil spill in what was described at the time as the highest fine ever imposed on a company in US history.

Jiji Press reported Friday that the High Court had denied the tsunami was a predictable event.

- 'Take responsibility' -

Footage broadcast on Japanese networks showed the plaintiffs holding a banner calling for an even higher damages order of 22 billion yen.

"Take responsibility for the Fukushima nuclear accident!" their banner said.

Three of the Fukushima Daiichi nuclear plant's six reactors were operating when a massive undersea quake triggered a massive tsunami on March 11, 2011.

They went into meltdown after their cooling systems failed when waves flooded backup generators, leading to the worst nuclear disaster since Chernobyl.

Overall the tsunami along Japan's northeast coast left around 18,500 people dead or missing.

In March, Japan's top court said it had finalised the acquittal of two former TEPCO executives charged with professional negligence over the Fukushima meltdown.

The decision concluded the only criminal trial to arise from the plant's 2011 accident.