Otago Corrections Facility general manager Lyndal Miles said two staff from the facility near Milton remained in hospital last night.
Their injuries were not life-threatening, Ms Miles said.
The alleged assault took place as the prisoner’s cell was being unlocked about 1.30pm, she said.
Other Corrections staff members, who were nearby, immediately rushed to the aid of their colleagues and secured the prisoner, who was relocated to the management unit and would be charged with misconduct.
"All assaults on our staff are unacceptable," Ms Miles said.
Corrections Association of New Zealand national secretary Mark Duncan, who is an Otago Corrections Facility senior Corrections officer, said the alleged attack highlighted the nature of the work environment that Corrections officers faced on the job.
"Our thoughts go out to the two officers and members of the Corrections association who were assaulted today in what can only be described as an unprovoked and cowardly attack," Mr Duncan said.
"These sorts of attacks, which unfortunately are not uncommon, highlight the environment that these brave officers work in to protect the public.
"We will stand by our members and ensure they have full wrap-around support as they recover from their injuries.
"These injuries can impact both physically and mentally."
Ms Miles said police would determine if any criminal charges would be laid.
A review into the incident would be commissioned.
The staff members would be supported by Corrections managers and the organisation’s welfare team, Ms Miles said.
They would not return to work until they were ready.
Corrections officers dealt with "some of New Zealand’s most challenging people, and do an exceptional and brave job in often very difficult circumstances", she said.
"Prisons can be volatile environments."
Many prisoners could behave unpredictably and act without warning.
More than 80% of prisoners had convictions for violence in their offending histories.
More than 90% had a diagnosis of a mental health or substance abuse disorder.
Additionally, 35% had a gang affiliation, "which is a known predictor of violence".
"The reality is the threat of violence is something we cannot eliminate entirely, but we are constantly working to ensure our prisons provide the safest environment possible for staff and prisoners," Ms Miles said.
Corrections had invested in training and tools to keep its people safe, she said.
Last night, a police spokeswoman confirmed an investigation was under way.
