A staff member at Whanganui Prison required stitches after being assaulted by an inmate at the Kaitoke facility.
It was one of seven cases of assault on 11 Whanganui Prison staff in the past month, six of which occurred in the past week.
The incidents come in the wake of a report by Chief Ombudsman Peter Boshier last month which shone the spotlight on high levels of violence at the prison.
In it, he said there was "a clear and urgent need for the prison to address the levels of violence and intimidation".
Chief custodial officer Neal Beales said no staff member had been hospitalised as a result of the most recent incidents.