The Auckland City Library says it is trying to save several historical newspapers that have been water damaged.
The Auckland Council says a sprinkler on the third floor activated on Friday afternoon due to a rupture in the system.
Water soaked through to the basement and fire fighters had to use specialist equipment to drain water from soaked items.
Libraries and information manager Allison Dobbie says the computer system, printers and carpet have also been damaged.
Ms Dobbie says experts are trying to assess whether the historical newspapers can be saved and many are irreplaceable.
The library will be closed until at least Monday.