The blaze was reported about 4:45 a.m. local time in an area of the Universal City property that includes working sets and sound stages, popular sites for tram passengers from the nearby Universal Studios Hollywood theme park.
The fire also damaged the clock that allowed Michael J. Fox to travel "Back to the Future'' and the New York and New England street scenes, spokesman Eliot Sekuler said.
NBC Universal hadn't determined the cost of damages, Sekuler said.
As many as 50,000 videos and reels, including every film made by Universal, and television series such as "I Love Lucy,'' were damaged, NBC Universal President and Chief Operating Officer Ron Meyer told the Associated Press. Duplicates are stored at a separate location.
The fire burned as many as four acres of the 391-acre lot, or about two city blocks, said Universal spokeswoman Cindy Gardner.