A man facing a serious violence charge was mistakenly released from a Serco-run prison, the Weekend Herald has learned.

The embattled private prison operator, which last year lost its contract to run Auckland's Mt Eden prison, has now been penalised more than $19,000 for the wrongful release.

Joshua Calthorpe had been due to finish a prison sentence at Auckland South Corrections Facility in Wiri in April.

But he was still to be dealt with on charges of aggravated robbery, blackmail and obtaining by deception, and should have been transferred from Auckland South Corrections Facility - operated by Serco - to a remand cell until that offending was dealt with.

Advertisement

Instead he was released and spent two weeks at large before police returned him to custody, a source told the Weekend Herald.

Calthorpe was yesterday sentenced to almost six years behind bars for the aggravated robbery and blackmail charges, and will also serve a shorter sentence concurrently for the obtaining by deception charges.

He has previously spent time on the run from police in 2012 and last year, after failing to appear in court.

A Serco New Zealand spokeswoman confirmed yesterday a prisoner had been "wrongly released" in April.

"He had completed his sentence, but faced new charges and should have been detained on remand. We alerted the police as soon as the error became known and he was subsequently returned to custody."

The spokeswoman said ensuring public safety was Serco's first priority.

"We undertook a review of the event, to identify how it occurred and prevent such an incident occurring again."

Justice Minister Judith Collins said Calthorpe's release was "not acceptable". She said Corrections had penalised SecureFuture - the consortium that owns the Serco-run Wiri prison - $19,581.59 for the wrongful release.

Labour's Corrections spokesman Kelvin Davis said Serco needed to "get its act together".