The bird was spotted on Wednesday last week in the industrial area of Øra in Fredrikstad, and was then seen again on Sunday night.
"I cannot not tell you how exciting it is. People have come in to Norway in private jets just to see it with their own eyes," bird watcher Rune Asbjørnsen told NRK.
"This is a very big thing from an ornithologist's point of view. There has not been such a rare bird seen in Østfold since the song sparrow was found on Akerøya in 1975."
The Trumpeter Finch, a small passerine bird in the finch family, has been increasingly spotted in Northern Europe since 2005, a shift that has been attributed to climate change.