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

Los Angeles -

A tree that fell on the tracks of a roller coaster at a southern California amusement park may have caused the ride to derail, the Los Angeles Times reported on Tuesday.

The accident happened on Monday evening at Six Flags Magic Mountain, about 60km north of Los Angeles.

A tree, estimated to be 12m high, had fallen on the tracks, the paper reported, citing Peter Melton with the California Division of Occupational Safety and Health.

“It looked like a pine tree fell, and it fell across the track of the Ninja ride,” Los Angeles County Fire Inspector Rick Flores told broadcaster KTLA.

The tree caused the first car of the Ninja ride to derail, leaving 22 people stranded for nearly three hours in the roller coaster cars, 12m off the ground, the Los Angeles Times reported.

Four people had minor injuries, and two were transported to a local hospital, the paper said, citing Magic Mountain spokeswoman Sue Carpenter.

“We were riding on the Jet Stream when we saw the Ninja go into the trees,” Brandy Chambers the TV station.

“It was a lot of leaf noise and then cracking noises... and a lot of screaming.”

The ride remained closed for further inspections. - Sapa-dpa