A passenger was reported to have been bleeding from the head and it was reported that one woman had hit her head so hard on the panel above her head that it cracked.
The pilot declared a medical emergency in Billlings.
KTVQ in Montana reports that local paramedics responded to the scene to find three crew members and a number of passengers injured.
United Airlines released this official statement:
"The flight encountered severe turbulence upon descent into Billings, Montana. Three crew members and a number of passengers were injured. Our primary focus is assisting our employees and passengers who were injured, and our flight safety team will review what happened."
Bil Dahlin, a passenger on the flight told KTVQ that he felt the crew was as surprised by the sudden drop and turbulence as the passengers.
"I think they were somewhat panicked," Dahlin said. "I think they were trying to assess things themselves so they really didn't offer any explanation because of what happened so quickly."