A former Fukushima nuclear plant worker has been diagnosed with radiation-linked cancer, Japanese authorities said on Tuesday, the first such confirmation more than four years after the worst atomic accident in a generation.

An official with the health ministry said the ex-employee, who was in his 30s while working at the plant following the 2011 crisis, has developed leukemia. He is now 41 years old, local media reported.

"The case has met the criteria" to link his illness to the accident, the official said on condition of anonymity, adding that other possible causes have been ruled out.