Private prison operators Serco have failed to meet several key performance measures since taking over running the Mt Eden Corrections Facility, a Corrections Department report shows.
The report, released under the Official Information Act, shows two wrongful releases and one wrongful imprisonment in the eight months since the Mt Eden facility was handed to the British-based company.
It was fined $150,000 when Aaron Stephen Forden, a prisoner dubbed "Houdini", escaped earlier this year.
All of the incidents are listed as zero tolerance areas under Corrections Departments standards.
Corrections chief executive Ray Smith told Radio New Zealand Serco's failure to meet several performance measures was "less than we expect".
"We have been actively working with Serco to ensure that improvements are achieved."
Other results showed an 82 per cent completion rate on random drug tests at the facility - 17 per cent short of the standard required.
Targets for prisoner management plans and telephone call monitoring were not reached.
However, random drug testing showed only a three per cent return of positive samples.
The Public Service Association said the results showed the failure of privatising prisons.
National Secretary Richard Wagstaff said Serco had jeopardised public safety by allowing wrongful releases and escapes.
"The department may be trying to write these off as 'teething problems' but they are no such thing - these are core procedures that should be right from the start.
"This report shows Serco is failing in its number one priority - to keep the public safe."
Mr Wagstaff said the report showed the "folly" of opening another private prison at Wiri.