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.
"However, one staff member received stitches to a cut lip following an assault and was attended to at the local accident and emergency clinic."
Other, more minor, cases in the past month included a prisoner flicking water from a mop at a staff member and another throwing a spice sachet at a Corrections officer.
Whanganui Prison said it had ramped up efforts to curb violence after the September report.
Beales said assaults on staff by prisoners could be spontaneous and without any warning and Corrections held a zero tolerance to violence policy.
"No assault or violent behaviour is acceptable . . . any prisoner who resorts to violence will be held to account," he said.
"Corrections officers come to work every day to keep New Zealanders safe. They do an exceptional and brave job in often very challenging circumstances.
"Our staff work with some of New Zealand's most difficult and challenging citizens."
Corrections accepted 33 of the report's 37 recommendations and said it was already taking action.
Beales said the prison was implementing a "long-term" gang engagement and management and anti-bullying strategy.
Whanganui Prison has about 544 prisoners and 241 fulltime front-line staff.
Just under 40 per cent of the prison population has a violent offence as their current conviction. More than 75 per cent have a history of convictions for violence.
"Gang prevalence and influence is also a contributing factor to the rates of violence in prison and gang members are disproportionately identified as responsible for assaults in prison," Beales said.