Private prison operator Serco says its response to illegal activities at Mt Eden Prison will be robust, systematic and sustained, after flying in a top regional official.
Serco is under investigation by the Department of Corrections and the Ombudsman after footage of inmates fighting, smoking cannabis and drinking alcohol was shared on social media.
Warning: the video below contains graphic images, which may be disturbing to some viewers.
The company's Asia-Pacific director of operations, Scott McNairn, said in a statement the company was fully co-operating with the investigation, as well as conducting its own.
"Along with senior colleagues, I have been in regular contact with Department of Corrections management. We have provided them with a clear action plan to demonstrate that our operational response will be robust, systematic and sustained."
Mr McNairn said Serco received a report from Corrections on allegations of organised fights in prisons two months ago, but decided they were unsubstantiated.
He said the company was committed to being held to account by the investigation, which would report its findings on 28 August.
"We do not underestimate the challenge of operating this prison. We hold 976 of the country's most difficult and challenging individuals. As an inner city remand prison, we manage tens of thousands of prisoner movements every year.
"Preventing violence, attempts to smuggle contraband and other criminal activity inside the prison walls is a daily reality. Our managers and staff work incredibly hard to manage these challenges. There is always more that we can do, and we are getting on with it," said Mr McNairn.
Prime Minister John Key said the review into illegal activities at Mt Eden Prison would be thorough.
He said the Government had a duty of care to make sure prison inmates were safe.
"One big advantage we have with Serco and privately run prisons is we do have clauses within the contract that well and truly allow us to take action if that is justified and required, so I don't know the circumstances of how widespread it is or where it's actually happening, but we want to get to the bottom of it."
Mr Key said the Government could impose financial penalties on Serco for any breaches of its contract.
The Department of Corrections said it was disappointed the critical report into the running of Mt Eden prison was not handed to the company running the prison until 10 months after it was completed.
Corrections head Ray Smith said he had been in touch with Serco's global chief executive and Mr McNairn had flown into Auckland yesterday to oversee an overhaul of security at the prison.
Mr Smith said he had heard rumours of an organised fight club inside the prison, and was aware of a report about it done 12 months ago, but there was never any evidence until the video emerged.
"The fact that this has managed to finally produce some evidence, I hope that we can get to the bottom of it and maybe there are police charges that are going to follow this."
Mr Smith said Serco topped prison league tables, but he was unhappy with its handling of the problems at Mt Eden.
"What I saw in terms of that video footage was the kind of thing that worries anyone that runs a prison system and I was very, very unhappy about it."