Books by prominent Hong Kong pro-democracy figures have become unavailable in the Chinese-ruled city's public libraries as they are being reviewed to see whether they violate a new national security law, a government department said on Sunday. Hong Kong public libraries "will review whether certain books violate the stipulations of the National Security Law," the Leisure and Cultural Services Department, which runs the libraries, said in a statement. "While legal advice will be sought in the process of the review, the books will not be available for borrowing and reference in libraries.”