Film writer Glenn Erickson has identified scenes of Mexican citizens running away from the robot that were originally photographed in Hawaii for the 1956 release The Revolt of Mamie Stover (1956).
The communication console and screen from Klaatu's saucer featured in El día que paralizaron la Tierra (1951) can be seen directly in the background of Labcentral's Astro Physics Laboratory where Vera Hunter and Dr. Hubbell Eliot have their confrontation. A map of the world has been placed behind the glass.
After a string of highly successful big budget science fiction films throughout the 1960s, Twentieth Century Fox considered remaking this film in the early 1970s in response to the energy crisis. The project was not green-lighted and, by the end of that decade, accepted an offer from Wade Williams to buy the film and all rights. This film is now part of the "Wade Williams Collection."
Spyros Skouros, then president of 20th Century Fox, liked the concept and reportedly urged the production of this film.
The long shots of Kronos moving were accomplished by animation, presumably the work of animator Gene Warren.