11:03 AM PT -- Fort Lauderdale PD is saying this brawl has nothing to do with their city or their beaches -- so it's unclear where exactly this happened ... but it's still pretty crazy all the same.

Spring Break's looking more like a UFC match as all-out mayhem erupts on South Florida beaches ... and the good people of Fort Lauderdale are probably saying, "Thanks a lot, Miami!!!"

The annual college student getaway kicked off Monday with thousands of students making their way to FL, and it almost immediately got outta hand. Multiple bikini-clad students went toe-to-toe in the sand -- as the video shows, it quickly turned into a melee involving dozens.

No word on what exactly sparked the brawl, but we're guessing alcohol played a part.

This is exactly the kinda scene Miami Beach feared when the city imposed new restrictions ahead of Spring Break -- but, as you can see, the madness has just moved up the coast a bit to Lauderdale.

Miami's decision came after 2 shootings during last year's break, which also resulted in 488 arrests ... and more than 230 of them were felony cases.

As we reported ... the city posted a campaign video where spring breakers were urged to take the party elsewhere and informed there would be threatened curfews, bag checks, restricted beach access and DUI checkpoints.

All vibe killers, so it's no wonder Fort Lauderdale is absorbing the massive party scene.

One day in, and that city has already had to ramp up the police presence ... putting more officers in the sand to patrol beach parties, and K-9 units were inspecting sunbathing revelers.

Cops or not, one thing's already clear -- when the crowds gather, there's gonna be fighting.