This video - from viewer Mark Bloomfield - shows people gathering outside, as fire crews tackle the blaze on the National Library of Wales' roof.
It is thought that nobody will be allowed back inside the library until tomorrow.
Workers were all evacuated after the fire broke out.
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Eight members of a multi-million pounds drug gang operating out of Cardiff have been jailed for a combined total of 54 years.
Ex-convict could have been suffering from drug-induced "excited delirium" when he attacked and killed a young woman, an inquest has heard.
New figures show that council tax in Wales remains lower than in England.