Jackie Armstrong, 35, was quickly rushed to hospital after plummeting to the ground inside Zippos circus tent at Winter Wonderland in Hyde Park, London.
Spectators were quickly ushered out of the tent after the dramatic fall - during the aerial acrobatics show.
Paramedics were seen moving the "highly experienced" performer through a shocked crowd outside.
One trader at the much-loved seasonal carnival said the response was "very professional."
The Bratwurst salesman, who wished not to be named, said: "There was a huge crowd outside the tent and security guards had to clear a path out the way.
"It was a really busy night and there were a lot of people at first but they managed to get her to the ambulance quickly.
"Then she was inside for a while. It was all well handled and very professional."
Another, selling warm winter clothes beside the tent, said he didn't see the fall or emergency response for himself but said the performers he had met were "lovely."
He said: "One of my customers told me what happened last night. I hope she's alright, it's terrible."
Jackie, who was performing with Zippos Circus Cirque Berserk show was taken to hospital but her condition is unknown.
A spokesman for W, the PR company representing Zippo's Circus said: "The fall was from no more than 12ft, versus the 36ft stated in some media outlets.
"Zippos Circus can confirm that an aerial artist fell during the 6pm performance of Cirque Berserk at Hyde Park Winter Wonderland.
"The female British artist, Jackie Armstrong, performs an aerial act and is a highly experienced circus artist with 10 years in the ring.
"Jackie was immediately attended to on the scene by first aiders and an ambulance called. She was taken to hospital by ambulance and further information on the nature of her injuries is awaited.
"Immediately following the incident, audience members were asked to leave the Big Top and offered tickets for the next performance that evening."
Circus Founder and Director Martin Burton added: "Jackie is a very experienced artist whom we value dearly as part of our circus family.
"Clearly we are concerned and offering her and her family our full support and sympathy at this time.
"At this stage we cannot comment further as we have no information on any injuries she may have sustained."
Today, traders and visitors are carrying on as normal despite the terrifying incident.