A man and his daughter who had a child together have been told by a judge that their incestuous relationship must stop, the Otago Daily Times reported.

The 32-year-old man and 18-year-old woman admitted one charge each of incest, with the woman saying she was in love with her father and the pair had been living as husband and wife, the Otago Daily Times reported.

The relationship began when the daughter was 16 and lasted almost two years. Their child, a girl, was born a year ago, the Otago Daily Times reported.

During sentencing at Dunedin District Court Judge Stephen O'Driscoll told the pair: "This must stop. These sort of relationships do not last and are fraught with difficulties."

Counsel Bernadette Farnham, for the woman, said both offenders had "a mutual background of abuse and neglect". The woman had lived with inappropriate role models and inappropriate actions towards her by male members of her family, the Otago Daily Times reported.

Psychiatric and psychological reports indicated the pair had genetic sexual attraction, which sometimes happened between family members reunited after a long separation, the Otago Daily Times reported.

Judge O'Driscoll said that when the male offender was 13, he and his 30-year-old foster mother had started a sexual relationship. He was 14 when their daughter was born.

He had little to do with his daughter until she was about 16. He made contact in 2010, when a sexual relationship started, resulting in another child.

The judge convicted the daughter and sentenced her to 12 months' supervision, with a condition that she undertake counselling or treatment as directed.

The father carried a greater culpability in the relationship, the judge said, convicting the man and sentencing him to 300 hours' community work and 12 months' supervision. The father must complete a domestic violence programme, take other counselling as directed, and not be in the company of his daughter unless another approved adult was present.

The judge warned the pair, who have name suppression, they were "highly likely" to be sent to prison if they appeared again on similar charges.

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