Arwel Jones from the National Library of Wales told ITV News that he is hoping that the damage will be limited - "the most valuable stuff is housed in purpose-built cells at the very bottom of the library, and this fire is at the very top."
He admitted to concern that the damage from water pumped onto the building by firefighters would be as bad as the fire damage.
More top news
A group of women from Rhyl have formed their own support group to fight back against body shaming.
A proposal to remove to 53 public phone boxes from Neath Port Talbot, has been met with criticism from the town's Mayor.
People are requesting refunds for tickets to a popular Cardiff festival as the main act has been cancelled.