Kiley and Britney Neal were next in line when the Fire Ball ride at the Ohio State Fair sent eight people flying through the air, killing one.
The two teens watched in horror as the ride malfunctioned when a row seats snapped off as it swung back and forth.
An 18-year-old was killed after being thrown about 50 feet from the ride. Seven others, including a 13-year-old, were injured. Fire officials say five are considered to be in critical condition.
"All of the sudden, the Fire Ball just went to the left and a few chairs -- it looked like they were kind of falling out -- and then it went to the right and the whole row fell out," Kylie Neal said. "We heard them hit the ground and everything."
The teens said the ride operator hit the emergency stop button when he noticed somebody had started to fall out.
"Somebody started to fall out so the guy panicked and hit the emergency stop, and I think the momentum made the whole seat fall off," Britney Neal said.
The teens said the other riders were silent as the ride came to a stop. But the riders were forced to remain in their seats for about five to 10 minutes, Kylie Neal said.
Britney Neal said she saw three people hit the ground, including the man who was killed. She said he hit a piece of metal and believes he died instantly.
"I know one of the guys in the seat had broken his leg, because it was all the way backwards," Britney Neal recalled.
"I was truly traumatized," she added. "This is actually one of my biggest fears, and I didn't actually think I'd have to witness it, especially right in front of me."
Ohio Gov. Kasich ordered all rides to be shut down until further inspection. The fair will open at 9 a.m.
The accident prompted California State Fair officials to close the Fire Ball ride there, according to the Associated Press.