Firefighters have rescued 24 people who were stranded on a roller coaster at a US amusement park.

Prince George's County fire officials say it took about five hours to rescue 17 adults and seven children from The Joker's Jinx roller coaster at Six Flags America in Maryland.

Assistant fire chief Paul Gomez says the riders were sitting upright near the top of the ride. A few had cramps, back pain and dehydration, but there were no major injuries.

A Six Flags America spokesman said it is not yet clear what caused the ride to stop but that it has a computerised safety system that "performed as it is designed to".

Six Flags' website says the ride goes 60mph and upside down four times.

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