"The person was transported to Auckland City Hospital where, after undergoing surgery yesterday afternoon, they are in a serious but stable condition.
"No charges have been laid at this stage and we are still conducting inquiries into the circumstances of what has occurred."
Prison director David Pattinson told the Herald yesterday that staff immediately intervened and secured the alleged perpetrators and provided first aid to the victim.
"Corrections will also carry out a full investigation, and will ensure all evidence, including CCTV footage, is provided to police."
Pattinson said violence in prison was not tolerated.
"And anyone who resorts to this behaviour will be held to account, including facing criminal charges.
"Our staff manage some of New Zealand's most dangerous people in a complex and challenging environment."
Pattinson said over 75 per cent of the prison population had convictions for violence in their offending histories.