A cord wrapped around the 16-year-old's feet and severed them at her ankles while she was on the "Superman Tower of Power," a police dispatcher said. The girl was taken to a local hospital.

An unidentified witness told CNN affiliate WLKY she saw a cable on the ride snap.

"The people on the ride just came and hit the ground," she said. "When I got up there, the lady she was just sitting there, and she didn't have no legs. ... And she was just there, calm, probably in shock from everything."

"That could have been all of us -- riding that ride," witness Whitney Sandfer told CNN affiliate WDRB/WMYO.

The incident took place shortly before 5 p.m. ET, according to Six Flags spokeswoman Wendy Goldberg. The park remained open, but the ride in question was shut down and will remain so until the full investigation is complete, Goldberg said.

During the ride, passengers are lifted to 177 feet, suspended momentarily and then dropped, according to the park's Web site.

Passengers drop 154 feet at 54 mph, stopping "just 20 terrifying feet above the pavement," it adds.

"I seen the car go up. Then, like, the cable broke, I heard -- pwchh -- and I heard a lot of people screaming," Chris Stinnett, who was at a ride next to the Superman Tower of Power, told WDRB/WMYO.

"The cable went under the car -- and I seen it pull up and hit a lot of people -- and I seen them bring their legs up," Stinnett said.

The ride was introduced in 1995.