A wheel on one of the cars is thought to have disengaged from the rail, causing the Family Coaster at Arakawa Amusement Park in Arakawa Ward, Tokyo, to grind to a halt on Friday.
With seven adults and 12 children trapped on the ride five metres (16 feet) above the ground, the situation could have sparked panic.
However, thanks to the leisurely pace of the ride, the passengers initially weren’t bothered.
“The coaster was moving so slowly, I didn’t notice it had stopped,” a woman in her 30s and her six-year-old son who were on the ride at the time of the accident explained to local media.
The ride is billed on the park’s website as “the slowest rollercoaster in Japan” and is around 140 meters long.
Bemusement eventually turned to concern when workmen began to hit the train with hammers and staff attempted to push the train without explaining the situation to those still on board.
Customers called the emergency police number 110 and rescue crews arrived at the scene to help evacuate those stuck on the ride.
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Those involved in the incident are calling on investigators to examine the incident and find the cause of the malfunction to prevent the same problem occurring in the future.
No injuries were reported.