In this still image from video footage provided by KTLA-News, workers at the Six Flags Magic Mountain amusement park rescue people trapped on the Ninja roller coaster. Picture: KTLA-5 News

Santa Clarita, California -

A roller coaster hit a fallen tree at a US amusement park, dislodging the front car, leaving four people slightly injured and keeping nearly two dozen summer fun-seekers hanging up to nine metres in the air for hours as day turned to night.

Two of the four people hurt on Monday on the Ninja coaster at the Six Flags park were taken to hospital as a precaution, but all the injuries were minor, fire and park officials said.

“We were going across one turn and all of a sudden a loud noise happened,” Jeremy Ead, one of the injured riders, told KCAL-TV. “I ducked down just in time. A hard branch hit me in the head. I was there bleeding from my head, which was a little worse than this,” he said, pointing to a gash in his forehead.

Peter Melton, a spokesman for the Division of Occupational Safety and Health, said on Tuesday that the ride will remain closed until investigators determine exactly what went wrong.

The Six Flags Magic Mountain coaster hit the fallen tree at about 5.30pm and stopped, said Michael Pittman, a Los Angeles County Fire Department dispatch supervisor. It was nearly three hours later before all 22 of the riders were rescued.

At least one of the cars, which are normally suspended beneath the track, was dangling at an angle, derailed at the front.

Firefighters and park maintenance workers in harnesses removed the riders one by one. The riders waited patiently as firefighters tried to reach them through a tangle of track and trees, some talking with each other and others resting with their eyes occasionally closed.

All were alert and communicated with park staff during the evacuation process, the California park said in a statement.

The accident comes just over a week after dozens of people were stranded more than 60m up on a revolving tower at SeaWorld San Diego for hours. Authorities there said a power failure stalled the ride.

In July of 2013, a woman was ejected from a roller coaster at Six Flags Over Texas in Arlington and died. The death was ruled an accident, but her family has sued both Six Flags and the German company that built the coaster's trains, both of whom denied any wrongdoing.

In September 2012 at another Southern California amusement park, Knott's Berry Farm, riders were left dangling at 90m for more than three hours when its Windseeker ride broke down. No one was injured in that breakdown. - Sapa-AP