Two state jails have worse assault rates than the controversial privately-run Mt Eden prison.
Radio New Zealand reported today that the worst overall assault rate in the year to June was at Christchurch Women's prison, with 37 assaults per 100 prisoners.
Hawke's Bay Regional prison was next with a rate of 23.5 assaults.
Mt Eden prison, which has come under the spotlight following revelations of fight clubs and violent attacks on inmates, came in third with a rate of 22.9.
The prison, run by private company Serco, although currently under management from Corrections while investigations into the prison are ongoing, recorded 224 assaults by prisoners on each other or on guards.
Radio NZ reported the assaults ranged from minor spitting or pushing to those requiring hospital treatment and ongoing medical supervision.
Corrections Association President Beven Hanlon told Radio NZ "it's clear Serco are trying to get people to under report" assaults at Mt Eden.
And despite this, the prison was still near the top when it came to rates of assault.
Mr Hanlon said the figures likely showed more serious assaults in Mt Eden and more minor ones in state-run prisons.
"It appears that Serco are under reporting all of their incidents," he said.
"It was reported the other day that a prisoner had his arm broken in two places, and it was recorded in a High Court note, yet it wasn't recorded on his [prison] files."
Prisoners being thrown of balconies were also not recorded by Serco.
Mr Hanlon said Christchurch Women's prison was small, so a single assault would push up its rate, while Hawke's Bay was home to the highest number of gang members.
When asked if it was surprising a women's prison topped the list, Mr Hanlon said women were often jailed for serious offences. It was harder for women to be imprisoned in the first place and they had reasons, such as childcare, to avoid incarceration at sentencing.
"I think there's still some sexist views out there - just because they're women, they're nice people. If they're in prison, they're not in prison because they're nice people."
Mr Hanlon called on prison staff to be allowed to carry pepper spray.