The Friday night confrontation was caught on camera by French journalist Eric Morillot ... who says the argument quickly turned physical after Cannes Director Thierry Frémaux was zipping around outside the Carlton Hotel, where a good chunk of attendees is staying.

Morillot says the Cannes honcho asked the cop for his name after apparently denying him the spot ... getting more and more heated as the bickering went on -- even threatening to file a complaint.

Of course, all the shouting's happening in French, but tension like that is a universal language. The heat reportedly died down later, with the 2 shaking hands.

For what it's worth, Frémaux announced at the beginning of this festival he'd be riding around on his bike to reduce his carbon footprint ... but it's unclear if he'll be making the switch back to cars now.

As you know, Frémaux's been welcoming the likes of Harrison Ford and Johnny Depp to the festival this year -- with both actors getting standing ovations after their films were shown in front of esteemed audiences.

Martin Scorsese is the latest to touch down in France ... bringing "Killers of the Flower Moon" to the festival Saturday -- and the cast joined him, including Leonardo DiCaprio, Robert De Niro, and Jesse Plemmons.