Vandals have flooded Portsmouth's main library causing substantial damage.
An investigation has been launched into the flood, believed to have started on Wednesday in the third-floor toilets of the building in Guildhall Square.
Books, including first editions by the authors Charles Dickens and Arthur Conan Doyle, were undamaged by the leak.
However, water caused electrical damage and has forced the building to close until repairs are completed.
Works by the authors, along with one-off naval documents, have now been moved to a secure lock-up until the library reopens.
Library services manager Lindy Elliot said: "This water had cascaded through the whole building, so we have got considerable water damage throughout the whole of the site.
"It's a very, very wet and dangerous building."
It's believed the library could be closed for more than a week to allow the carpets to dry out.
Officials are waiting for CCTV equipment to dry out in order to analyse footage to catch those responsible.
Nearby Elm Grove Library in Southsea has extended its opening times.
Police said the incident was reported on Friday afternoon and officers were investigating.