Six people who were living in Fukushima at the time of the 2011 nuclear disaster and have since developed thyroid cancer have filed a lawsuit demanding compensation for their illnesses.

The people, now aged 17-27 and living in and outside of Fukushima, demand the Tokyo Electric Power Company Holdings pay a total of 616 million yen ($A7.6 million) in compensation.

They say their illnesses were triggered by massive radiation spewed from the Fukushima nuclear plant.

One of the plaintiffs, identified only as a woman in her 20s, said she has had to prioritise her health over her career and has seen prejudice against thyroid cancer patients.

"But I decided to come forward and tell the truth in hopes of improving the situation for nearly 300 other people also suffering like us," she said.

Their lawyers said it is the first group lawsuit in Japan filed by Fukushima residents over health problems linked to the nuclear disaster 11 years ago.

In a news conference after filing their lawsuit at the Tokyo District Court, a plaintiff and the mother of another plaintiff said they hoped the court would establish a correlation between the cancer and radiation leaked from the plant.

An expert panel commissioned by the Fukushima prefectural government has so far ruled out the alleged cause.

The plaintiffs, who were six to 16 years old at the time of the meltdown, were diagnosed with thyroid cancer between 2012 and 2018, their lawyers said.

Four of them had their thyroid fully removed and need to take lifetime hormonal treatment.

One of them says the cancer has since spread elsewhere.

The other two had part of their thyroid removed.

More than 290 people have been diagnosed with or are suspected of having thyroid cancer, including 266 found as part of the Fukushima prefectural panel's survey of some 380,000 residents aged 18 or younger at the time of the disaster.

The occurrence rate of 77 per 100,000 people is significantly higher than the usual 1-2 per million, their lawyers say.

Prefectural officials and experts have said the high detection rate in Fukushima is due to overdiagnosis in many cases, which might have led to unnecessary treatment or surgery.

The government at the time of the accident was slow in its emergency response, and evacuation in many places was delayed due to a lack of disclosure about what was happening at the plant.

Residents trying to flee in their cars clogged roads and were stranded for hours outside while radiation leaked from the damaged reactors.

Some residents headed to evacuation centres in the direction of the radiation flow.