A zero tolerance stance is being taken by bosses at Mt Eden prison following the release of footage showing prisoners fighting.

Footage has emerged on YouTube showing prisoners engaging in fights while being cheered on by other prisoners.

In a statement Serco Director of Operations Scott McNairn says he has commissioned a thorough investigation into the incident.

He says assaults, fights in prison, and the smuggling of mobile phones are "illegal and unacceptable".

The company's vowing to work with the Department of Corrections to prevent further incidents.

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