The plaintiffs, now aged between 17 and 27, were living in the Fukushima region in March 2011 when an earthquake triggered a tsunami that lead to the disaster.

They are seeking 616 million yen (£4m) in compensation from Tokyo Electric Power Company (TEPCO) and will file a class-action lawsuit at Tokyo District Court on Thursday, according to Japanese media reports.

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An expert investigation committee set up by the government has not recognised a causal link between radiation exposure from the Fukushima disaster and thyroid cancer, and a possible correlation could be the focal issue in the lawsuit.

The six plaintiffs were aged between six and 16 at the time of the nuclear disaster and were diagnosed with thyroid cancer between 2012 and 2018, The Mainichi reported.

Two of them had one side of their thyroid removed, while the rest had their thyroid extracted completely and need to take hormonal drugs for the rest of their lives, according to the newspaper. In one patient, cancer had spread to their lungs.

As of June 2021, 266 people had been diagnosed with thyroid cancer or suspected thyroid cancer following a Fukushima Prefectural Government survey on thyroid glands involving around 380,000 people who were aged 18 or under at the time of the disaster.

Lawyers claim that five of the six plaintiffs had their cancer detected in the survey. The other was diagnosed with cancer after voluntarily undergoing testing at a hospital.

The cancer discovery rate in the survey is several tens of times higher than usual, lawyers argue.

The prefectural government has pointed to the possibility of "overdiagnosis" through which many cancer cases requiring no treatment have been found, but the legal team says their clients' cancer progressed.

Lawyers have also highlighted that none of the six plaintiffs' cancer is hereditary, and argue it is highly likely that they developed the disease due to the nuclear disaster.

"Some plaintiffs have had difficulties advancing to higher education and finding jobs, and even given up on their dreams for their future," Kenichi Ido, the head of the legal counsel said.

TEPCO said in a statement that it would respond to the case sincerely after hearing the content of the claims and arguments in detail.