A prisoner injured in a gang-related assault at Auckland Prison is back behind bars after being rushed to hospital yesterday.

The man's condition was not believed to be life-threatening and he returned to the prison in Paremoremo last night and is being monitored by medical staff.

Chief custodial officer Neil Beales said an investigation will be held into the assault and police have been informed.

Beales said staff at the facility worked with some of the country's most difficult and challenging citizens.

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"Over 75 per cent of the prison population have convictions for violence and gang prevalence and influence is a contributing factor to the rate of violence in prisons."

The prison had a "zero tolerance" approach to violence, Beales said, and the perpetrator would be held to account.

The assault follows another gang-related attack at the jail this month.

And authorities had to intervene on November 12 when two inmates were attacked by other prisoners using makeshift weapons.