Four acrobats injured during a circus performance over the weekend in Rhode Island are listed in serious condition, the parent company of Ringling Bros. and Barnum & Bailey says. Four others are in good condition, and one has already been released from the hospital.

Feld Entertainment Inc., the parent company of Ringling Bros., issued a statement concerning Sunday's accident, in which the nine female performers, who were suspended from their hair 25-40 feet in the air, fell to the ground when the apparatus that was holding them failed. Two other circus members who were not part of the hair-hanging act were also hurt.

"The cause of the accident continues to be under review by both our company and outside authorities," Feld said in a statement Tuesday.

"It has been determined that a carabiner in the rigging failed, however we do not know at this point why," the statement said. "Each piece of equipment used in this act is inspected when it is initially rigged and visually re-inspected prior to each performance."

The Associated Press writes:

"Investigators suspect a snapped clip, which they found broken in three pieces on the ground, is to blame for the accident that occurred during a Sunday morning performance before 3,900 people, many of them children. The carabiner clip was one of several pieces at the top of a chandelier-like apparatus."When the clip snapped, the women fell 20 feet or more to the ground, and the apparatus landed on them."Relatives and rescuers say the women suffered injuries including a pierced liver, neck and back fractures, broken ankles and head injuries."Copyright 2016 NPR. To see more, visit