Mid and West Wales Fire and Rescue Service says 11 of its crews are continuing to fight the fire at the National Library of Wales.
It is advising people "to stay away for safety."
This video - from viewer Edward Mulgrew - shows firefighters pumping water onto the library roof earlier.
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Warburton went off in the second half during the Six Nations clash after he took a blow to his knee.
David Cameron says this should be a day for people to celebrate 'all that embodies Wales'.
Rain moving east, will spread across Wales in the first half of the night, some likely heavy.