A Brooklyn teen was beaten by a group of girls in a Flatbush McDonald's, police said Wednesday, but she is refusing to cooperate with authorities.

The vicious fight, caught on video, broke out at about 2:50 p.m. inside the 943 Flatbush Avenue restaurant on Monday, just steps from where the teens go to school.

The victim, a 15-year-old girl, appears to throw the first punch, said community advocate Tony Herbert. But she is then clobbered by a group of girls 16 to 18 years old.

"The bottom line is we have to say something so this doesn't give the precedent that this is OK to do," Herbert said, adding he has tried to reach out to the girl to convince her to talk to police. "Their hands are tied. She's not cooperating."

Herbert, who has been active in the community for years, said he spoke with police about the incident.

The fight goes on for over a minute until the girl falls to the floor, pulling off the shirt of one of her attackers in the process. The suspects continue to the kick the victim, before one girl, now clad only in a bra, stomps on her head.

Eventually, a few people pick the victim up off the floor and lay her down in a booth as she covers her face.

Police said neither the victim, nor the girl's mother are working with investigators.

The teens all appear to go to school inside the Erasmus High School building.

"Whatever it was, they just figured this would be the day to air it out," Herbert said. "That became a gang assault."