Four people suffered minor injuries after a St. Louis roller coaster at Six Flags stopped abruptly Friday morning.

The incident occurred on the Boomerang roller coaster at around 11:30 a.m. Six Flags said in a statement that the ride didn’t complete its normal cycle and stopped at a mid-point location. All the guests were able to safely exit the ride.

“Our First Aid staff responded immediately and four guests were transported to a local medical facility as a precautionary measure,” the company said in the statement. “The safety of our guests is our top priority and the ride will be closed for a thorough inspection before re-opening.”

The Six Flags park isn’t officially open to the public. However, choirs from several schools in the area were at the park for a music festival, Fox 2 Now reported. Other students were there for “Outdoor Classroom Days.” All students had access to several rides and games.

The ride is described as “gravity defying” and pulls its riders backward up to the top of a 125-foot lift hill. The riders are then released along a 1,650-foot twisted steel track at speeds up to 50 mph.

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