They are refusing to say what the operation is related to but it is suspected to involve drugs.
Police said that search warrants had been executed in Auckland Prison, Spring Hill Correction Facility in Waikato and at residential properties around Auckland.
Around 180 police, customs and correction staff were involved in the investigation which was to do with recent activity by some inmates at Auckland Prison, a police spokesman said.
Police were talking to several prisoners in the East and West Wings of the top security Auckland Prison. They would make further comment after the outcome of today's investigation.
