"He hit the ground with real force. It looked really horrible. He was conscious the whole time but he really bled," said Marcus Rosendahl, spokesman for Circus Maximum.
The teenager was taken to the Astrid Lindgren Children's Hospital in Stockholm. A hospital spokesperson said his injuries were not serious.
The 15-year-old is part of an eight-member Chinese acrobatic troupe, the Flying Warriors. When the accident happened he was working on a bar eight metres from the ground. He threw himself in the air to be caught by another artist on a trapeze, but for some reason he hit his head on the bar with great force and fell onto the safety net six metres below.
"When you fall in an uncontrolled way you can bounce out of the net. Thankfully he didn't do that," said Rosendahl.
The boy was admitted to the Karolinska University Hospital just after 6pm. The Circus Maximum big top was full of spectators, with around 1,200 people including many children witnessing the accident.
"A murmur went round the tent. It was a bit of a shock," said Rosendahl.
Asked what the minimum age was for circus artists, Rosendahl said he could not answer, but said that nobody under the age of 15 worked at Circus Maximum.