DENVER -- Three crew members and "a number" of passengers were injured Monday when a United Airlines flight encountered severe turbulence, a spokeswoman for the airline said.
The captain declared an emergency on United Flight 1676, which was flying from Denver to Billings, Montana, said United's Christen Davis. The flight met turbulence as it descended.
"Our primary focus is assisting our employees and passengers who were injured, and our flight safety team will review what happened," the spokeswoman said.
The Federal Aviation Administration said the pilot "declared a medical emergency after a flight attendant was injured by turbulence. The plane landed in Billings without incident."
United says five people were taken to St. Vincent Healthcare in Billings. A flight attendant had head injuries and she was in critical condition Monday night. Two other crew members and two passengers were treated and released from that hospital.
There were 114 passengers and five crew members onboard, including passenger Bill Dahlin.
"There was a lot of screaming, a lot of hollering," he told CNN affiliate KTVQ.
Dahlin said one woman hit the ceiling so hard that the ceiling cracked. He said he thought the crew was just as surprised by the sudden turbulence as the passengers were.
"I think they were somewhat panicked," KTVQ reported 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."
Other witnesses described a baby flying out its parent's arms and landing two rows back. The parent didn't know where the baby was for a short time.
Others on the plane say the turbulence was so severe that it felt like the jet was out of control for a minute. They believe it happened over Wyoming as the plane was about to start its descent into Billings.
Last month, a United Airlines flight returned to Newark Liberty International Airport in New Jersey after turbulence injured five flight attendants.
The plane hit "severe turbulence" about 45 minutes into the Beijing-bound United Flight 89, said Ron Marsico, a spokesman for the Port Authority of New York and New Jersey, which operates the airport.
CNN contributed to this report