One man has been killed and seven others injured after a thrill ride broke apart, throwing them up into the air.
Video captured by a bystander at the Ohio State Fair fair shows the Fire Ball ride swinging back and forth like a pendulum and spinning in the air before it crashes into something and part of the ride flies off.
Screams are heard as passengers are thrown to the ground.
"The fair is about the best things in life, and tonight with this accident it becomes a terrible, terrible tragedy," said Republican Governor John Kasich.
Officials said the man who was killed was one of several people who were thrown to the ground when the ride malfunctioned. They have not released his name.
Ohio State Medical Centre said three of the injured were being treated there. Two of them were in critical condition, the hospital said.
Officials did not know what caused the ride to break apart, saying the investigation was ongoing.
"Of course we want to get to the bottom of this," Mr Kasich said, noting that there could be things to be learned that could help other fairs and amusement parks. "Make no mistake about it, it's a very, very sad night for all of us."
A Columbus fire official told WKRC-TV that the man killed was 18 and that the seven people injured ranged in age from 13 to 41.
Kaylie Bellomy was in the next group waiting to board the Fire Ball.
"It was going for a minute and it was at its highest point and I saw somebody fall on the ride, and then a minute later the whole like row of seats fell off and hit the ground," Ms Bellomy told WCMH-TV.
It was chaos afterwards, she said. "Everybody was running. I got ran over trying to get out of the way."
A company providing rides at the Ohio State Fair this year describes the Fire Ball as an "aggressive thrill ride."
The company's description of the ride said it swings riders 40 feet (12 meters) above the midway, while spinning them at 13 revolutions per minute.
Ride inspectors did not notice anything out of the ordinary when they conducted their inspections and cleared the Fire Ball for passengers, said Director of Agriculture David Daniels.
Michael Vartorella, the state's chief inspector of amusement ride safety, said the Fire Ball was inspected three or four times before the fair opened.
Officials said none of the rides would be open until they are all fully inspected.
The Ohio State Fair, which is one of the largest state fairs in the US, runs until 6 August.
Additional reporting by AP
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