Japanese police have arrested a high-ranking yakuza over claims he sent workers to Fukushima for the radiological clean-up without a licence, the first arrest of a mobster in connection with the nuclear plant.

Officers in northern Yamagata prefecture were quizzing Yoshinori Arai, a 40-year-old senior member of a local yakuza group affiliated to the Sumiyoshi-kai crime syndicate, a police spokesman said Thursday.

Arai allegedly dispatched three men to Fukushima to work on clean-up crews in November last year, he said.

Under Japanese law, a government licence is required by anyone who acts as an employment agent.

Arai is also suspected of sending people to work on the construction of temporary housing in the tsunami-hit northeast, the spokesman said.

Arai reportedly told police that he intended to profit from the scheme by taking a cut of the workers' wages. Those employed at Fukushima earn more than others in similar work because of the potentially hazardous nature of the job.

It was the first arrest of a mobster linked to Fukushima clean-up, the police spokesman said.

A Japanese journalist who worked at the crippled nuclear plant months after the accident in March 2011 has claimed that Japan's yakuza are involved in supplying clean-up crews.

The journalist, Tomohiko Suzuki, told AFP the crime groups have long sent debtors to nuclear power plants as a way of paying off loans made at sky-high rates.

Like the Italian mafia or Chinese triads, the yakuza has engaged in activities from gambling, drugs and prostitution to loan sharking, protection rackets, white-collar crime and business conducted through front companies.

The gangs, which are not illegal, have historically been tolerated by the authorities, although there are periodic clampdowns on some of their less savoury activities.