A Corrections officer has described working with some of New Zealand's worst inmates, saying the prison system is a "pressure cooker" that's going to blow.

Jails across the country are short hundreds of frontline staff, despite burgeoning prisoner numbers - and several staff have contacted Stuff claiming they're being put in harm's way. Corrections denies the prison system is short-staffed.

"The current prison situation with the muster crisis can't go on," said a female Corrections officer who contacted Stuff. "It's a pressure cooker right now. It's going to get to a point where it will blow.

"All my fellow officers and I can do is be there. We try to minimise the damage, protect the public and hope, at the end of the day, we can all go home to our families."

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The officer said her prison, which won't be named to protect her identity, is short-staffed and employees are leaving "because the job gets more and more dangerous".

IAIN MCGREGOR/STUFF About 27 per cent of Corrections officers are women. One female officer says the job means being sexualised by inmates on a daily basis.

"I'm out there alone in the compound with just my wits, my training, radio, vest, cuffs and a can of pepper spray."

The department's latest annual report showed 988 Corrections officers were women - about 27 per cent of all officers.

The officer said being a female employee in a prison means hearing sexual comments from inmates on a daily basis. But she still loved her job, finding encouragement in the chance of rehabilitating a small number of prisoners.

ANNA LOREN/STUFF The officer says staff are leaving as the job gets "more and more dangerous".

"As a woman in a men's jail I can tell you I have been assaulted. I have been propositioned. I do hear comments of a sexual nature daily. And yet I'm still here.

"There are the few that we can help turn their lives around. We try every day to get these guys to think and make better choices. Most don't. But every now and then, one does. That's why I do what I do."

She said a 600-bed prison at Waikeria announced by the Government for completion by 2022, would not put a dent in the country's prison muster.

SUPPLIED Corrections chief custodial officer Neil Beales maintains the prison system is not short-staffed.

"I see the types of people we house. I handle the rapists. The murderers. The paedophiles. I handle other people's nightmares.

"Where else are we meant to house these people? Those that oppose prisons, well, where are we supposed to put these offenders? The guys that try to spit on you when you walk past; the guys that openly tell you they will re-offend once they are out."

The impending closure of Waikeria's high-security unit would mean the new 600-bed prison would simply be replacing beds, she said. The prison system would only be about 100 beds better off.

"The original [National Government-proposed] 1500-bed unit is what is required," she said. "It's not a political thing. It's not a game. It's a major safety concern.

"We have more police on the streets, which can only be a good thing. But more police means more arrests, which means more prisoners. And we have nowhere to put them."

In response to the officer's comments, Corrections chief custodial officer Neil Beales said the prison network is "not short-staffed," and "continues to operate safely and securely".

"Corrections officers do an exceptional and brave job every day in helping to keep New Zealand safe in often very challenging circumstances," Beales said.

"We have recruited almost 1500 new Corrections officers since 2016 and we are continuing our recruitment process due to the increasing prison population."

Beales also said that in the last financial year to date there were eight serious assaults on staff by prisoners, down from 17 the previous year.