Two teenage boys had to be rescued when a “reverse bungee” ride failed at Winter Wonderland in London, leaving them suspended in the air in a cage.
The teenagers were on the ride at Hyde Park on Wednesday evening, when the Met Police said the incident occurred.
The amusement park industry’s own regulatory safety scheme said there was a “technical issue” with a gear-box.
Winter Wonderland said both boys were “safely” escorted off the ride.
It added the ride would be closed while an investigation took place.
The Met Police said it had attended the scene, along with London Fire Brigade, but the cage had been lowered down before they arrived, the boys had left the scene and there were no reported injuries.
The Health and Safety Executive (HSE) has been informed, a Met spokesperson said.
Becky Littlewood, who filmed video showing the cage hanging in the air, travelled from Suffolk to go to Winter Wonderland with her husband.
She said: “We were walking around where the rides were and I really wanted to go on it but my husband said, ‘no, it doesn’t look safe’.
“We watched it for a while and then as we turned around there was a massive bang and it was hanging on the side – two people on the ride were screaming.
“Then it looked like they tried to reset the ride, as [the boys] were being pulled up into the air.”
“Security came running and started pushing us back, telling us to stop filming.”
She added: “I wont be going to Winter Wonderland again.”
London Fire Brigade confirmed on Twitter it had attended the incident but had not needed to respond.
The Amusement Device Inspection Procedures Scheme, which went to the site on Thursday morning, said in a statement released via Winter Wonderland: “We can confirm that the elastic cord and the steel wire rope supporting the reverse bungee gondola in which the public sit has not snapped or failed in any way.”
The organisation, which monitors the safety of amusement park rides, added: “We inspected the ride at 07:00GMT this morning and it was found that a technical issue had occurred within a sealed gear-box that controls the release of the elastic cord and steel wire rope.
“The HSE has been informed.”
A Hyde Park Winter Wonderland spokesperson said: “We can confirm that a technical issue involving the reverse bungee occurred on Wednesday evening.
“Both riders were safely escorted off the ride, checked by our on-site medics and were not injured.
“Safety is our highest priority and the ride is closed while further investigation takes place.”
They added: “All of our rides undergo rigorous and regular safety checks by experienced members of staff trained in health and safety.
“We also provide regular training for all staff to ensure our visitors can enjoy a fun and safe experience.”