The university's vice-chancellor, Professor Stuart McCutcheon, said the changes would save several million dollars. This would be spent on academic activities.
He said the university's financial situation necessitated making difficult choices.
Governments led by both Labour and National had favoured policies that reduced the cost of university study for students and the Government, over polices that enhanced the quality of universities.
That meant New Zealand universities' levels of income per student were among the lowest in the developed world.
"We could deal with this by increasing class sizes ... but that would reduce the quality of our teaching and lower our international rankings.
"The only alternative approach, and the one we have adopted, is to reduce costs of support services."
He added that there had been a major shift towards students' digital access to library materials.
McCutcheon dismissed reports of book-burning and the indiscriminate destruction of books. He said such methods would not form part of the relocation of the three libraries' collections.
"Any removal of books will be done as part of the standard library practice of removing material that is damaged, unnecessarily duplicated, or significantly out of date."
The storage space at the university's Tamaki campus currently held 700,000 items but had capacity for 2 million.
The student association's president, Anna Cusack, said the changes would "actively harm the future of creative arts at the university …"
She said thousands of students and leaders in architecture and planning, fine arts, and music and dance had expressed serious concerns about the proposal. These had been ignored.
"The outcome is completely against what students have been calling for at marches, sit-ins and self-led submissions for months."
She said the General Library was overcrowded "and has issues with accessibility".
The Herald has sought a statement from the Tertiary Education Union.
