The National Library of Australia and the National Film and Sound Archive of Australia (NSFA) have gotten a tick of approval after an Auditor-General's report, released Monday, showed the two institutions had largely done a good job at managing their collections.

The audit office found both had systems and processes in place that complimented the large collections but could work to improve on their efficiency.

But while the report's findings were mostly positive, it also highlighted some concerns about the long-term storage of the growing collections.

The National Library has four facilities for its 279 shelf kilometres of items, which it estimates will grow two-to-three shelf kilometres every year for the next two decades.

The facilities include the main building in Parkes, a Library-owned repository in Hume, a leased Hume Annexe and a short-term leased space at the National Archives of Australia (NAA) in Mitchell.

It's the collection at the leased space that will soon have no home if arrangements can't be made within the coming years.

"The Library is unable to extend the Mitchell lease beyond 2025 as the NAA will require the space," the report said.

"The Library advised that unless additional facilities can be found it will not have storage for 47 kilometres of collection material currently housed at these two locations."

The NSFA's storage woes were less of an issue due to a digitisation strategy but the report noted it had "no formal or consistent process" for acquiring high volume items.

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It comes less than a month after the National Gallery of Australia told senators it backed a proposed bill that would allow it to host part of its unused collection outside of the ACT.

The existing legislation allows all national institutions to use storage facilities outside the nation's capital but the art gallery is excluded from that exemption.

Gallery director Nick Mitzevich said the bill's changes would allow the institution to free up space on site and save money on storage costs.

"It's more financially advantageous to be able to seek commercial storage out of Canberra because the market is more competitive," Mr Mitzevich said.

"Taking up storage in other regional centres or in capital cities will mean that we can be much more efficient in our storage costs."