Video taken by audience members shows a curtain dropping to reveal several performers hanging from an apparatus suspended from above. Seconds later, as they begin to perform, the women fall, and the metal apparatus lands on them.
Rosa Viveiros of Seekonk, Massachusetts, said she saw that the acrobats had fallen on top of at least one other performer below, a man who stood up with his face bloodied. The acrobats remained still and did not get up, she said.
"Everybody thought maybe it was part of the act, but then when they landed on the floor, they weren't moving, they weren't getting up," she said. "Then we knew that there was something wrong."
Viveiros attended the circus with her husband, their 6-year-old grandson and 9-year-old niece.
"Everyone was in shock," Rosa Viveiros said. "It was pretty overwhelming to see that."
Othello Smith was watching the performance with his family.
"You could tell the crane was heavy, because it took 10 guys and you could see them struggling to lift it from on top of the girls," he said.
The Associated Press contributed to this report.