National Library of Wales fire 'worst moment in its history'
The fire that destroyed part of a roof at the National Library of Wales has been called "the most difficult moment" in its 100-year history.
Library president Sir Deian Hopkin aired his concern in his first public comment since Friday's blaze.
He also thanked those who had supported the Aberystwyth institution described as housing many "national treasures".
An investigation is under way after a section of roof on what is known as Building Two was gutted.
A small part of the library collection is thought to have been damaged.
The fire affected an area largely used as office space and for new acquisitions.
The library was closed to the public on Saturday and will remain shut on Monday, but it could reopen on Tuesday.
Up to 300 staff and 100 visitors were evacuated when the alarm was raised at 14:40 BST on Friday.
It took about 50 firefighters nearly four hours to bring it under control.
A specialist salvage company from Oxford has been assessing the damage caused to the collection.
Sir Deian said: "I would like to express my relief at the news of the safe evacuation of the library when the alarm was raised and on behalf of the library I would like to thank the Mid and West Wales Fire Service for their prompt attendance and their efforts in extinguishing the fire.
'Could be much worse'
"I would also like to thank the many individuals and organisations for their immediate offers of material assistance and for their expressions of concern at this most difficult moment in the library's history."
Arwel Jones, director of public services at the library, said on Saturday that water used to fight the flames had leaked through five or six floors.
"That's damage to the structure of the building and to the offices and, of course, any collections that were being worked on at the time," he added.
"As far as we can ascertain at the moment the damage to the collections is limited. This isn't storage facility - it is office space - so it could be much, much worse than it is."
Mr Jones said the library would be open to staff on Monday and around 70 would be relocated after their offices were damaged by the fire.
Workers had been repairing the roof near to where the fire started, but the library said it was "not in a position to draw any conclusions from this".
Reports from the scene suggested a 100ft (30m) section was destroyed.
Mr Jones described the library's significant collection as the "memory of the nation".
He said it contained six million books, a million photographs, 30,000 manuscripts, works of art and maps.
Many of the library's books were unique and would not be found elsewhere, he added.
Firefighters, some from as far afield as Carmarthen 50 miles (80km) away, attended the scene along with 11 fire appliances, and it was not until 18:30 BST on Friday that the blaze was put out.
Library staff said it was not known how the fire started, but everyone was safe.
Aled Gruffydd Jones, who takes over as head librarian in August, said on Friday that he was puzzled by how the fire could have started. "Clearly we need an inquiry," he added.
The Aberystwyth University sports centre, which is next door to the library, was closed as a precaution.