One person was killed and seven injured Wednesday after an amusement ride malfunctioned on opening day of the Ohio State Fair, one of the largest state fairs in the country.

Battalion Chief Steve Martin, a spokesman for the Columbus Fire Division, said the victims were hurled from the Fire Ball ride at 7.20pm local time. One man was killed on impact, the Columbus Dispatch reported.

"This is the worst tragedy in the history of the fair," Ohio Governor John Kasich said at a news conference. Kasich called for a full investigation and ordered all rides shut down until safety inspections could be made.

"It's kind of hard to imagine you have family that goes to a state fair and those calls come, that there was a terrible accident, a terrible tragedy, and someone you love is involved," he said.

Three of the injured were taken to Ohio Health Grant Medical Centre. Two were later released with one patient in critical condition, a hospital spokesman said.

Another four were brought to Ohio State University's Wexner Medical Center, where Dr David Evans told reporters that "multiple passengers were ejected at high speed, at high energy more than 20 feet [6 metres] or more."

He said four patients were in intensive care, one of whom was in surgery. The victims vary in ages from teenagers to at least one in their 60s.

"We will get to the bottom of this. There will be complete transparency," Kasich added.

Republican Senator Rob Portman also issued a statement, saying he and his wife send their "deepest sympathies to all those who were impacted by the accident."

The swinging Fire Ball pivots and swirls as high as 40 feet [12 metres] at 13 revolutions a minute, according to specifications from Amusements of America, the carnival operator that deployed a fleet of rides to the fair.

Videos circulating online and on local news stations show a sense of chaos as the incident unravelled. In one video, the six gondolas with four seats each rocketed from the top of a parabolic arc. At least two of the gondolas appear to smash into a metal structural support beam, as one drops away. One person appears to have been launched into the air as the video ends in screams from onlookers.

Amusements of America did not return a call for comment. Organisers of the Ohio State Fair did not immediately respond to a request for comment.

Travis and Mitch Taylor, 18-year-old cousins from a town outside Columbus, said they rode the Fire Ball Wednesday night just before the fatal incident. They contemplated climbing back on but instead opted for food, backpedalling away from the ride as they watched those who boarded behind them climb into the air.

"We just watched the people get scared," Travis Taylor said.

The ride swung high to the right and back to the left, then suddenly people were free-falling.

"It very well could have been us," Travis Taylor said.

Onlookers screamed and cried, the cousins said, and almost immediately police and EMS began blocking off the crowd from those who were injured.

"Everyone was just scared as heck," Mitch Taylor said. "We were shaking."

The cousins weren't sure how long the Fire Ball had been operating at the Ohio State Fair, but they said it had been there for the eight years they had been attending. It was one of their favourites, they said.

"You see those videos of a roller coaster malfunctioning," Travis Taylor said, "but you never think it can actually happen."

Michael Vartorella, a ride inspector, said at the news conference his team oversees 4300 pieces of equipment in the state, which are carefully inspected to ensure working condition of electrical systems, hydraulics and structural integrity. The Fire Ball was inspected three or four times before the fair began, he said.

Vartorella became emotional as he described the stakes of the safety of those rides.

"My grandchildren ride this equipment," he said. "We take this job very serious, and when we have an accident like this … it hits us really hard."

The governor sought to downplay concerns of fair guests, some of whom have bought season passes, who may think twice before returning to the fair that runs until August 6.

"We'll move on but it doesn't mean we don't grieve for what happened," Kasich said.

"I'll be at the fair," he said.

Washington Post