"Ghostbusters: Frozen Empire" fired up the box office this weekend, and the whole franchise passed an impressive milestone ... but some are saying producers shouldn't count their ghosts before they materialize.

According to reports, 'Ghostbusters' is projected to make $45.2 million in its opening weekend domestically -- taking the top spot by a wide margin over some incumbent champions of the theater.

Meanwhile, the movie got off to a mediocre start internationally ... taking home just $16.1 million in 25 global markets -- still, enough for an impressive opening weekend total of $61 million.

'GFE' fought off both "Dune: Part Two" and "Kung Fu Panda 4" for the top spot this week -- there are certain indicators the film may not be a total box office smash.

For one thing, 'Frozen Empire' is only slightly outperforming the last film in the franchise -- "Ghostbusters: Afterlife" -- by about $1 million domestically ... and that was significantly cheaper to make with reports saying it cost $75 million to the new movie's $100 million budget.

And, "Ghostbusters: Frozen Empire" has got some mighty competition at next weekend's box office -- with the combined forces of Godzilla and King Kong slated to premiere.

BTW ... critics and audiences have very different opinions on the movie. It's got a critics score of 43% on Rotten Tomatoes but an audience score of 84%. So, maybe not a cinematic masterpiece, but probably one hell of a fun ride!