Four ex-bosses of Tokyo Electric Power Company (TEPCO) were ordered to pay the damages in a suit brought by shareholders over the nuclear disaster triggered by a massive tsunami.

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

They went into meltdown after their cooling systems failed when waves flooded backup generators.

The accident was the worst nuclear disaster since Chernobyl and prompted the declaration of an evacuation zone around the plant.

Around 12 percent of the Fukushima region was once declared unsafe but no-go zones now cover around two percent, although populations in many towns remain far lower than before.

TEPCO has been pursued in the courts by survivors of the disaster as well as shareholders.

It is currently engaged in a decades-long effort to decommission the plant, a costly and difficult process.

The tsunami that set off the disaster left 18,500 people dead or missing.

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TEPCO - TOKYO ELECTRIC POWER