New Zealand education and immigration officials are investigating "worrying concerns" about an unregistered Auckland-based Japanese academy after one of its students was found dead last week, it was announced Monday.

Nozomu Shinozaki, 22, from Yokohama, was found dead with head injuries Wednesday at Columbus Academy in West Harbor, West Auckland.

Assault and kidnapping charges have been filed against nine Japanese students at the performing arts academy aged between 17 and 26. The academy's director, Katsuo Kanamori, 49, has been charged with attempting to obstruct justice after allegedly telling his students not to cooperate with police.

The academy is not registered as a private training institute and has not been approved as an education facility, Education Minister Trevor Mallard said.