The rear car of an amusement park roller coaster separated from the others and tipped over Sunday, and officials said 18 people suffered minor injuries.
The roller coaster at Valleyfair amusement park was close to pulling into the station when the rear car separated, tipped and came to rest on its side on a platform.
Valleyfair spokesman Bill Von Bank said it was not immediately clear what caused the car to detach, but riders said it happened after the one in front of it experienced a problem.
"It started jerking and moving around, like, not right," said Katelyn Churchich, 16, of Oakdale, who was in the second-to-last car. "We kind of heard scratching and we didn't know anything was wrong until we smelled metal grinding with each other, and then when we looked back, one of the cars was tilted on its side."
Bailey Merchant, 12, of Shakopee, said she was in the rear car when the car in front started jerking and smoking. She said she fell out of her car when it tipped.
"We were jerked and twisted and it started to hurt really badly," she said.
Fourteen people were taken to St. Francis Regional Medical Center, where they were treated for mostly strains and sprains and released, hospital spokeswoman Lori Manke said. Four people refused medical attention, Von Bank said.
The roller coaster, the Wild Thing, has six cars and was carrying 35 people at the time of the accident. It reaches speeds of up to 74 mph but was braking and going much slower as it approached the station, Von Bank said.
Valleyfair, which is owned by Cedar Fair LP, of Sandusky, Ohio, said its maintenance officials were investigating and the ride was closed until further notice. The suburban Minneapolis park remained open.
Von Bank said the Wild Thing had been in operation for 10 years without any similar problems.
The park later said in a statement that two sensor faults caused the computerized safety system to shut down the ride twice Saturday. Both times, it said, maintenance staff found no problems and the ride was reopened. The ride was shut down for 10 minutes less than two hours before Sunday's accident for a routine inspection, but no problems were noted, the statement said.