A teacher has resigned from Kings High School in Dunedin after disclosing a sexual relationship with a student.

Intimate photos have emerged of the teacher at the centre of a Dunedin high school sex scandal, appearing to show her in bed with a student.

One of the pictures, which Stuff has chosen not to publish, appear to show the former King's High School employee in bed with a student.

Another picture, which appears to be a selfie of the teacher, had the caption "Well I have keys...and after hours Acces [sic]."

The Education Council had been informed about the sexual relationship.

A spokeswoman on Monday said an investigation into the matter would be carried out.

The school's rector, Dan Reddiex, confirmed the female teacher had resigned after disclosing the nature of her relationship with an 18-year-old student on Wednesday.

Reddiex said the teacher told the school "that she had an inappropriate relationship of a sexual nature with a senior student in 2015," adding the student was not a minor.

"Upon making this disclosure she was immediately suspended and has subsequently resigned from her teaching position at King's acknowledging that she has overstepped professional boundaries," he said.

"Our first priority is the safety of our students and we are extremely disappointed at the actions of this former staff member.

"We are confident through our investigation that the incident in 2015 was isolated to one student who was then enrolled at King's."