Paremoremo prison was put on lockdown after three guards were attacked by five inmates in the maximum security C Block, the Herald understands.
A prison guard was hospitalised after the attack by inmates at Auckland Prison, in Paremoremo, but has since been discharged.
Two others were taken to an accident and emergency clinic, assessed and treated.
Inmates in other wings were causing a ruckus after they heard the emergency call over the speaker system.
A source said they could be heard "banging things in unison".
The prison was locked down soon after the emergency call was made.
Emergency services were called at 1.50pm, and took one patient to North Shore Hospital in a moderate condition.
The Department of Corrections said: "All staff were wearing stab-proof vests and were assessed by medical staff on site.''
The staff member taken to hospital has since been released.
The other two were taken to an accident and emergency clinic, assessed and treated.
Yesterday, Corrections' northern regional commissioner Jeanette Burns said the injuries were not life threatening.
Police are investigating, but are yet to confirm if charges have been laid.
"No assault or violence is tolerated in prison. Any prisoner who uses violence will be held to account," Burns said.
"Corrections deal with some of society's most difficult and challenging offenders. Violence is not tolerated but unfortunately from time to time does happen."
The Herald understands all inmates were locked in their cells at 2.45pm yesterday and were only unlocked just before 10am today.
The guards were attacked in C Block, a maximum security wing where only six of the 12 resident inmates are unlocked at once.
C Block has been sealed off and the police are at the scene.
According to Corrections 2014/15 annual report, the number of non-serious and no injury assaults on staff and prisoners have increased between 2013/14 and 2014/15.
"While this is a matter that requires further strategic focus, it can be seen in the context of improved reporting as a result of the campaign to make violence in prisons unacceptable," the report stated.
"It may also be linked to the increasing number of prisoners on remand (and with indicators of high-risk and complex needs), as these individuals do not have access to the full range of rehabilitative programmes, can be suffering from recent abuse of alcohol or drugs and can be volatile as a result of uncertainty while awaiting trials or sentences."
The last high-profile attack on a prison guard was in May at the Serco-run men's jail at Wiri when drunk prisoners allegedly attacked a guard.