Inmates at an Auckland prison are holding organised fights, filming them on contraband mobile phones and uploading the footage to the internet.
The footage has emerged on YouTube and clearly shows gang members engaging in one-on-one fights while being cheered by other prisoners.
Clothing worn by those in the videos is printed with "SERCO MECF", suggesting the fights are taking place at Mt Eden Correctional Facility in central Auckland.
Mobile phones are banned in prisons and TVNZ said it was unknown how the footage made its way online.
University of Canterbury Criminologist, Professor Greg Newbold - who served seven years in prison - said the footage was "disgraceful".
"This is something I have never, ever seen in prison before," he told TVNZ.
"To have something like this going on in a prison without any staff intervention is disgraceful. There is no other word for it.
"It shows management breakdown. When inmates can stage these types of events without any knowledge of the staff or any intervention from the staff it shows the staff aren't doing their jobs and the responsibility for that lies with management."
The prison is run by Serco, a UK firm contracted by the Department of Corrections.
Serco director of operations Scott McNairn told TVNZ the incidents were being investigated and the company was working with Corrections and police.
Additional security measures had been taken and access to exercise yards was "further limited".
"For many prisoners, violence is the norm. We have work and education programmes to address this behaviour, but remand prisoners, about 80 per cent of those we hold, are not obliged to take up these opportunities."
Corrections also told TVNZ it was investigating.