(ABC News)

A frightening accident at a St Louis-area haunted house left a 17-year-old girl hospitalized.

It happened at Creepyworld, a popular Halloween attraction in Fenton, Mo., that bills itself as “America’s biggest and scariest Screampark.” According to the Jefferson County Sheriff’s Department, the girl was working as an actress in the haunted town last Thursday night, when she somehow got a noose that was being used as a prop wrapped around her neck.

“The noose was hanging over a bathtub, Sheriff’s Department Capt. Ron Arnhart said. “For whatever reason, her head wound up in the noose and it looked like she lost her footing and slipped off the edge of the tub.”

A co-worker who makes rounds to check on employees found the teenager, whose name has not been released, unconscious and hanging.

“She’s been moved out of the Intensive Care Unit, and her medical condition is improving,” Arnhart said. “Our investigation is ongoing, but at this point we believe it was a terrible accident.”

Investigators say the girl was working in that section of the house of horrors by herself. Police don’t know if any visitors to the haunted house might have witnessed the injured teen struggling for help, or if they might have thought it was all part of the frightening show.

“We very much hope this young lady makes a full recovery,” Arnhart said.

Police say Creepyworld employs nearly 100 workers, and draws huge crowds every Halloween season. A YouTube video posted on the park’s website shows haunted houses filled with dismembered body parts, zombies, a torture chamber, murderous bikers armed with chainsaws and a haunted pig farm. Like most elaborate haunted houses and amusement parks, Creepyworld’s website warns anyone with asthma, seizures or a heart condition to steer clear.

Calls and emails to Creepyworld and its media representatives were not returned.