A staff member at Christchurch Men's Prison died suddenly while on site yesterday.
Stuff reported a guard died while undertaking the physical readiness assessment (PRA).
Chief custodial officer Neil Beales said it happened after a suspected medical event.
"His colleagues immediately called an ambulance and began CPR, but despite all efforts, staff were unable to resuscitate him.
"We are deeply saddened by this tragic loss, and our thoughts are with the man's family and friends. Support is being provided to his family and colleagues."
Beale said a decision was made to temporarily suspend the PRA while inquiries are made.
It affects all prison sites across the country.
"This decision reflects the unknown nature of how the death occurred, and gives time for Corrections to look into the processes and protocols surrounding the PRA."
Corrections will be undertaking its own internal review of what happened.
"If there are any factors that require attention, Corrections will take action immediately to address these."
Worksafe has been notified and the Coroner may also conduct their own investigation into the matter, Beale said.
"We continue to send our deepest sympathies and condolence's to our staff members family and friends at this very difficult time, and continue to provide support to them and his colleagues."