A prison officer who died after an alleged assault from an inmate had concerns for his safety and was seeking to join a growing list of staff transferring to other jails.

Jason Palmer, a father of two young children, had spoken to relatives about the lack of protection for officers dealing with prisoners at Spring Hill Corrections Facility in North Waikato.

His death has sent shockwaves through the community of prison officers, and their union is now warning the handling of this case by those in charge could trigger an exodus from the profession.

Mr Palmer, 33, a former US Marine who moved to New Zealand before marrying his Kiwi wife Tracy, was one of three officers unlocking a prisoner's cell on Saturday when he was allegedly punched to the floor, and hit his head.

He suffered severe injuries and his life support was switched off on Sunday.

A 21-year-old man accused of assaulting Mr Palmer appeared in Hamilton District Court yesterday. He was given name suppression and will be held in custody.

Mr Palmer's mother, Ada, told TVNZ from Virginia that her son had told her he did not carry anything or have any helmets or face guards, or shields to hold. "It was all just, as he described it, a sort of a hand-to-hand combat situation."

Her family was not coping well, she said. "We're trying madly to get some money together so we can get over and attend his funeral."

Beven Hanlon, of the Corrections Association of New Zealand, said the circumstances of Mr Palmer's death were tragic "but the circumstances that led up to it were 100 per cent avoidable".

Corrections Department chief executive Barry Matthews said he was extremely disappointed and angry that Mr Hanlon had "taken this tragedy and used it to push his own agenda".

Spring Hill is designed for low security with an emphasis on preparing inmates for release. But the Herald understands several guards have left in recent months amid safety concerns, and Mr Palmer had also looked into a transfer.

The inmate Mr Palmer was dealing with had been put into the "general population" while the management unit that would normally house him was being expanded to allow double bunking, Mr Hanlon said.

Had the inmate been in the management unit, the tragedy would not have occurred, he said.

"When he wants to eat, all we do is we open a slot in the door - which is big enough to get a meal in - and then we close the slot, so he can't punch us."

Mr Matthews and Corrections Minister Judith Collins had stated there was always a potential risk to prison officers. "We're exceptionally scared by those comments," Mr Hanlon said.

"Those comments could result in an exodus of prison staff. I work in the prison system - that's got me thinking 'holy shit, someone's just been killed' and they're saying, well that's an acceptable risk."