Visitors Paul Clark, his wife Jiorgia, and their four children had come from Washington state on holiday. The family saw firefighters battling the blaze while they were on the London Eye on Saturday.
“It was sad to see,” Mr Clark told BBC. He said they were worried the artwork had been damaged, but were “very relieved” it was all safe.
Mr Clark said he is a huge fan of Vincent Van Gogh – the gallery houses the painter’s famed Self-Portrait with Bandaged Ear.
The fire broke out in the west wing of the building, which is mostly used for offices and storage.
The director of Somerset House Trust, Jonathan Reekie, said there were “no valuable artefacts or artworks” in that part of the building.
The Courtauld Gallery is an art museum that houses the collection of the Samuel Courtauld Trust, including masterpieces ranging from the Middle Ages to the 20th century. The gallery also features works by impressionists Edouard Manet, Claude Monet and Paul Cezanne.