Local media reported the duelling appeals, filed Wednesday, with a court official confirming the decision had been appealed but declining to provide details.

The Tokyo district court on July 13 ordered four ex-bosses of Tokyo Electric Power Company (TEPCO) to collectively pay 13 trillion yen in damages to the utility for failing to prevent the disaster caused by a March 2011 tsunami.

The suit against them and one additional former executive was filed by a group of shareholders seeking to recover losses sustained by TEPCO because of the meltdown, which was the world's worst nuclear accident since Chernobyl.

The court sided with their claim that the former executives failed to listen to research and carry out preventative measures like placing an emergency power source on higher ground.

Instead, when a 9.0-magnitude offshore quake triggered a massive tsunami, it swamped the Fukushima Daiichi nuclear plant, which went into meltdown and spewed radioactive material that forced evacuations within a 20-kilometre (12-mile) radius.

In a statement issued Wednesday, the plaintiffs said they had appealed the court's July 13 decision, because it did not order damages from the fifth executive.

The damages award is believed to be the largest amount ever ordered in a civil suit in Japan and is meant to cover TEPCO's costs for dismantling reactors, compensating affected residents, and cleaning up contamination.

The figure is seen as largely symbolic as the executives are unlikely to be able to pay compensation even close to the amount, but the shareholder appeal asks the court to increase the damages to 22 trillion yen.

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TEPCO - TOKYO ELECTRIC POWER