A roller coaster at Thorpe Park was stopped mid-ride and passengers had to be walked down to safety after a guest put their leg outside the cart.
Riders were led from the Colossus ride after staff spotted a passenger putting their leg outside the ride on CCTV.
Park employees said no one was hurt.
A spokeswoman for Thorpe Park said: "We stopped the ride because a guest ignored our ride restrictions and put their leg outside of the cart while on board Colossus which was spotted by our vigilant staff on CCTV.
"Therefore we e-stopped the ride as soon as possible and evacuated all guests.
"Colossus is back up and running.
"All guests must keep their arms and legs inside the cart at all times when riding our rollercoasters."
The park is set to host the world's first "psychological" theme-park ride, created by illusionist Derren Brown.
Mr Brown said: “The process of creating this new experience has been the most challenging of my career – so much so that it has taken us three years to get the project on track.
"You can look forward to a heady mix of magic, suggestion, psychology, misdirection and showmanship.”
