The Education Council has confirmed that it is investigating allegations which are believed to involve a relationship between a 19-year-old woman and her former teacher.
The young woman's mother has told the Stuff news service that her daughter has left the country with her former teacher, who was described as a man "understood to be in his 50s".
The man had taught the young woman "for two years, before she reached high school", Stuff reported.
The Education Council said: "We can confirm the Education Council is investigating a lower North Island teacher, and the investigation has been ongoing since July 2017."
Although the alleged relationship is legal because the young woman is over the age of consent of 16, the Teachers Disciplinary Tribunal has previously ruled that relationships between teachers and former students can still be inappropriate.
Last year the tribunal, which is appointed and serviced by the Education Council, deregistered a female teacher at a youth justice residence after she married a male student who was half her age, even though both were adults by the time they married.
"This case shows that even when a teacher is no longer teaching a student, an intimate relationship may not be appropriate," the tribunal said then.
"Teachers retain a professional responsibility to their students, particularly those who are deemed vulnerable because of their age."