An AMC Theater in L.A. erupted into panic and confusion during an apparent emergency over the weekend -- a frenzied scene which might've actually affected one Martin Scorsese.

This all went down Saturday night at the AMC Century City location -- where eyewitnesses tell TMZ that all screenings around 7 PM PT were interrupted and cut short after a fire alarm started blaring throughout the entire facility ... the cause of which is still unclear.

We're told that AMC staffers weren't all that helpful in clarifying to people what was going on or what to do -- and folks started to shuffle out on their own ... heading into the lobby.

Our sources tell us, however, that some people were actually freaking out a bit -- seeing how no information was apparently being communicated, a handful of folks thought there might've been an active shooter situation ... so yeah, it sounds like it was a chaotic sitch.

We're told people were awkwardly standing around ... not really sure what to do. Eventually, though, a massive line formed once it became clear their movies were ruined -- and guest relations started to give out refunds.

Our sources tell us everybody there did eventually get their money back -- that, or a movie voucher for another visit -- and that even for the Taylor Swift movie, which is being sold as a premiere event was honored by the AMC staff ... but the whole process was messy.

The kicker to all this is that Scorsese was actually on hand Saturday night there at Century City -- as he was intro'ing a screening of "Killers Of the Flower Moon" around the same time.