Corrections Minister Sam Lotu-liga says the investigation into assaults and fight clubs at Mt Eden prison has been extended until the end of October.
Corrections took over the management of Mt Eden prison from the private prison operator Serco last month - after claims of violent attacks on prisoners and video footage of prison fight clubs being posted online.
Mr Lotu-Liga said the chief inspector of Corrections has asked for more time so the investigation could be thoroughly carried out.
Labour Party corrections spokesperson Kelvin Davis said the two-month extension showed what a circus there was at the prison.