TOKYO, Japan -- A Japanese language school has been removed from the immigration agency's list of approved schools after one of its staff was found to have restrained a Vietnamese student for several hours using a chain and padlock, local media said Wednesday.

The scrapping of the certification of the Nishinihon International Education Institute in the southwestern city of Fukuokaannounced by the Immigration Services Agency (ISA) on Wednesday is the first such measure taken by the agency since stricter standards for removal were outlined in 2016.

According to the agency, a Vietnamese student in his 20s was restrained in the teachers' room of the school for several hours in October last year.

The student, after finally being allowed to return to his dormitory, was then prevented from leaving by his assailant standing guard outside the room until the following morning.

The student was subsequently kept under surveillance the following day by the school official, according to media accounts.

Referenced by Japan's public broadcaster NHK as a human rights violation, the incident occurred after the Vietnamese student requested to change schools.

The agency said it has instructed the school, which has admitted it restrained the student, to now assist with more than 600 foreign students enrolled at the school to transfer to other schools.

Having been decertified as an approved school to learn Japanese by the ISA, the school will be unable to accept foreign students for five years.