Eleven female prison officers nationwide have reportedly been investigated for "inappropriate relationships" with inmates since January last year.
And at least four Spring Hill Prison officers and one at Waikeria Prison have either been fired or resigned in the past 18 months after forming relationships with prisoners, the Waikato Times reports.
The Department of Corrections made the revelation to the paper, but would not confirm the details of the cases.
However the Times reports two of the Springhill cases involved some physical contact between the officers and inmates, while the other two involve the smuggling drugs to inmates.
A corrections source told the paper one of the officers became involved with a Killer Bees gang member imprisoned for manslaughter and another one involved a prisoner serving grievous bodily harm.
A Corrections spokesman told the Times the majority of its more than 8,000 staff acted professionally, and breaches of the Code of Conduct were rare.