Arwel Jones, Director of Public Services at the National Library of Wales, told ITV News "our concern now is for the collection", and that it will take time for the extent of any damage to be estimated.
More top news
Andrew Price joins South Wales Caving Club to venture into the deepest cave in the UK
Any drizzle this afternoon will subside to leave a largely dry evening. Clearer skies in the north overnight.
Police were called to several Tesco stores in Wales to deal with chaos at midnight. Huge numbers hunted for bargains in shops and online.