The accident happened on the "Spinning Barrels" ride at the Holiday Park in Hassloch, Rhineland-Palatinate. The ride is similar to the fair ride known as "Breakdance", where groups of seats are spun around while individual seats, shaped like barrels on this particular ride, are also spun at increasing speeds.
It was not immediately clear what went wrong on the ride. But paramedics found the girl's body to be so badly mangled that they could only tell that the victim had died and was female, according to police at the scene.
"For now, we can only say there was an accident," a police spokesman told the news agency dpa.
The girl, who was from the state of Hessen, had been visiting the park with her mother.
Holiday Park is one of Germany's most popular amusement parks and is visited by about a million thrill seekers annually.