Hardened gang members sent south from the North Island due to overcrowding meant people were "walking on eggshells", he said.
Speaking on condition of anonymity, the OCF staff member said he agreed with those comments.
The case of Justin Soul Su'a, who late last year attacked a guard in a successful bid to get a transfer to a North Island jail, was not the only such incident, and was part of a growing pattern of violence and intimidation by prisoners sent south from other facilities, he said.
"I see it every day. We have had two serious staff assaults in recent times with North Island prisoners committing serious offences, just to get closer to families."
"Staff are verbally abused daily ... [it is] a very serious situation that is only going to get worse. An officer or prisoner will be seriously hurt or killed, I'm certain of it," the staff member said.
Shortly after the ODT learned of the two separate assaults by prisoners on OCF staff members this week, Mr Beales, of Wellington, again maintained there was no significant rise in violence or threats at the prison.
"I can confirm that there has been no evidence of a significant increase in threatening behaviour, or violence, at [OCF]"
However, prisons could be volatile environments where violence occurred out of the blue, as shown by the two incidents at OCF this week, where staff were assaulted by inmates without warning, he said.
The first came on Thursday in a therapeutic unit for prisoners vulnerable to self-harm or suicide, when staff asked a prisoner if he wanted to clean his cell.
"He declined and then assaulted staff without warning."
Two corrections officers were taken to hospital, and St John spokesman Gerard Campbell said one person taken to hospital from OCF that morning had suffered moderate injuries.
The staff are now recovering at home.
Mr Beales also confirmed that yesterday morning another prisoner punched a staff member in the face without warning, after he was unlocked to spend some time in the recreation yard.
The prisoner was immediately restrained and segregated by other officers. The assaulted officer was taken to a doctor for treatment for a cut lip.
The Corrections acting Regional Commissioner has requested a review of both incidents and police had been notified.
A new batch of 12 prisoners will arrive next week, on transfer from the North Island.
A Corrections spokesman confirmed 527 prisoners have been transferred from other prisons to OCF in the past financial year.
Mr Karetai and the OCF worker's views on the increased level of hostility at the prison were echoed by the father of a man on remand at OCF since August, who also spoke on condition of anonymity.
"Prior to Christmas, it's increased incredibly down there.
"[My son] has been the victim of ongoing threats and altercations with gang members.
"Where this Neil Beales from Wellington has got his information from I don't know, but he's totally wrong."
