An inmate is in a serious condition in hospital after an assault at Rimutaka Prison yesterday.
He was taken to Hutt Hospital, where he has been treated in the intensive care unit.
Corrections staff said the injured man was in a serious but stable condition.
Rimutaka Prison director Chris Burns said another prisoner was involved in the incident.
The case is being investigated and police have been advised.
Another inmate at the prison was injured in a suspected attack in May and was airlifted to Wellington Hospital for assessment and treatment.