The lost scenes of the 1927 movie Metropolis had their first public showing in Buenos Aires on Thursday. (Eduardo Di Baia/Associated Press)

A long-lost original cut of the classic sci-fi film Metropolis, with extra scenes, has recently been unearthed and screened for the first time in decades.

The original version of the 1927 film by Austrian-born director Fritz Lang was parked for 80 years, first in a private collection and then at the Museum of Cinema in Buenos Aires. That's where it was re-discovered in April with images that hadn't been seen since 1927.

"We no longer believed we'd see this. Time and again we had had calls about supposed footage but were disappointed," said Helmut Possmann, head of the Friedrich Wilhelm Murnau Foundation in Wiesbaden, Germany, which owns the rights to to the film.

Possmann said up to 25 minutes of extra scenes help flesh out secondary characters as well as the plot.

The cinema museum's director, Paula Felix-Didier, said theirs is the only copy of Lang's complete film and it is being guarded very carefully.

Metropolis was written by Lang and his actress wife, Thea von Harbou.

The film depicts a 21st-century dystopic world split into a class of underworld workers and an elite who control them.

Soon after its initial release, distributors cut Lang's masterpiece into a 114-minute version.

According to Felix-Didier, a private collector carried an original version to Argentina in 1928.

In the 1980s, Argentine film fan Fernando Pena heard rumours about a man who used to spend hours screening a version of Metropolis.

It took many years of begging by Pena, but employees at the Buenos Aires museum finally decided to check their archives this year to see whether they had a version of the film. In April, researchers uncovered the reels in the museum's archive.

In June, Felix-Didier carried a DVD copy of the long version to the Murnau foundation in Germany, where researchers confirmed its authenticity. As for a cinematic distribution, it's too soon to say whether the original will be re-issued.

"The film hasn't left the museum and it won't leave until the city government and the Murnau Foundation decide what to do," Felix-Didier said.

Possmann said it could take several years to restore the scratched film.

With files from the Associated Press