Police have made six arrests as part of an operation investigating historical sexual offending at Dilworth School in Auckland.

Auckland City Criminal Investigation Branch have been investigating since a complaint was initially made a year ago.

Six men have been arrested and charged on a number of serious offences that allegedly occurred across a number of decades from the 1970s to the early 2000s.

At this stage in our investigation we have identified 17 victims.

A 72-year-old, 73-year-old, 68-year-old, 69-year-old, 72-year-old and 78-year-old have been charged.

Dilworth Trust Board Chair Aaron Snodgrass said they understood criminal charges had been laid against persons formerly connected to the school relating to allegations of historical sexual abuse.

The Dilworth Trust Board "was saddened" to hear their Old Boys had allegedly suffered abuse while in its care.

He offered their apology to "any Old Boys who have been affected by abuse of any kind at our school".

"The Board considers all forms of abuse, including physical, emotional and sexual abuse unacceptable," Snodgrass said.

"Dilworth has sought not to have the school's name suppressed in connection with the proceedings as we want to discuss our response openly within our school community and Old Boys."

The current Royal Commission of Inquiry into Abuse in Care and learnings from similar inquiries overseas were pivotal in the School's decision to proactively address historical abuse with Old Boys and the wider community, he said.