The closure comes as students were preparing for HSC studies and younger children were looking forward to school holiday activities.

Manager of library services, Lyn Barakat, said the fire burned through boxes of returned books, melted shelving and set off automatic sprinklers that flooded the library.

‘‘It’s a huge impost on the community. This is an extremely well- used facility and all those who love it and come here regularly have been deprived of using it,’’ Ms Barakat said.

Police believe the fire started at about 9.20pm at the building on Croydon Street. It also caused smoke and water damage to computers and custom-made furniture in the new library.

A sprinkler system put out the fire before firefighters arrived but the water spread to every corner of the library.

Ms Barakat was thankful the shelves were a few centimetres off the ground and said the fire would have ‘‘completely wiped out’’ the library if the sprinklers had gone off in the main section of the building.

A Sutherland Shire Council spokeswoman said the council was doing its best to relocate students to nearby halls and encouraged people to use Caringbah, Miranda and Sutherland libraries in the interim.

Sutherland Shire mayor Councillor Carol Provan said someone must have seen what happened.

‘‘It is so disappointing that this has happened at our brand new library at Cronulla, that is such an important meeting place for our senior citizens and study area for our young people,’’ Cr Provan said.

Miranda duty officer Inspector Michael Merrett said police were looking at security footage and doing forensic testing at the scene.

Library staff will accept returned items in the foyer of Cronulla Central and people with items on hold could still collect them.

Anyone who saw people acting strangely on Croydon Street or in Cronulla Plaza between 9pm and 10pm should contact police.

Details: Crime Stoppers, 1800333000.

Where will you go while the library is closed during school holidays?