DENVER (AP) -- The government on Wednesday began investigating how a United Airlines jetliner hit severe turbulence on a cross-country flight over Kansas, injuring at least 22 and jolting one woman out of her seat so forcefully that she left a crack when she hit the side of the cabin, authorities and a witness said.
The Tuesday flight was the airline's third this year during which passengers were hurt because of turbulence.
The flight originated at Washington Dulles International Airport and was headed to Los Angeles. It was diverted to Denver International Airport, where it landed safely around 7:45 p.m. and was met by medical crews, Denver Fire Department spokesman Eric Tade said.
There were conflicting reports on injuries. Denver Health Medical Center said a total of 21 people were taken to five hospitals, and one other person was treated at the airport.
The Federal Aviation Administration said earlier that 30 were injured, one critically, but Denver Health officials said they had no record of anyone in critical condition.
At least 19 were released from hospitals by Wednesday morning, including a 12-year-old. Eleven had neck and back injuries. Hospitals declined to release the nature of the other injuries.
United spokesman Mike Trevino said four flight attendants were among the injured, but he had no other details.
Mr. Trevino said some of the passengers were placed on another plane with a new crew and left Denver on Tuesday night.
He said the plane that encountered turbulence remained in Denver overnight. Inspectors found "no obvious damage" to the plane's exterior, FAA spokesman Ian Gregor said.
The National Transportation Safety Board is investigating the incident, board spokeswoman Bridget Serchak said. FAA spokesman Mike Fergus said the incident would be a "front-burner item" for both the FAA and the NTSB.
Flight 967 was flying over Kansas at an altitude of about 34,000 feet when it hit the heavy turbulence, Mr. Fergus said. It was carrying 255 passengers and 10 crew members.
The turbulence was "just a huge up and down," said passenger Kaoma Bechaz, a 19-year-old Australian in the United States visiting her boyfriend.
Miss Bechaz told the Denver Post that the woman sitting next to her hit her head on the side of the cabin, leaving a crack above the window, and a girl across the aisle flew into the air and hit the ceiling.
Miss Bechaz said she wasn't thrown around because her seat belt was tight.
The crew decided land the Boeing 777 in Denver to tend to the injured, United Airlines spokeswoman Megan McCarthy said.
Mr. Trevino said he did not know where in Kansas the plane hit turbulence, but the National Weather Service said a line of strong thunderstorms extended from the middle of Missouri through the middle of Kansas on Tuesday evening. Thunderstorms, with updrafts of up to 100 mph, can cause bumpy rides for airplanes as they pass from an area of calm air to churning air, much like a speed boat hitting choppy waters, said Chad Gimmestad, a weather service meteorologist in Boulder, Colo.
Mr. Gimmestad said forecasters can't predict where those bumps will occur, so airliners generally try to fly around such storms.
The website FlightAware.com, which uses information from the FAA to track the path of aircraft, shows that the United jet flew south of a storm in Missouri and Kansas.
The plane entered Kansas about 90 miles south of Kansas City and flew for about 160 miles across the southeast corner of the state before crossing into Oklahoma. FlightAware's map shows the plane was about 90 miles north of Oklahoma City when it turned northwest toward Denver.
Tim Smith of Boulder was on United Flight 937, which also flew into Denver from Washington on Tuesday and landed after the diverted plane. He said his flight was delayed because of thunderstorms but didn't have any problems.
Mr. Smith saw ambulances and police cars surrounding a gate on the tarmac and one person on a stretcher when his plane taxied to the gate.
"Thank God I wasn't on that flight," Mr. Smith said.
In February, about 20 people were hurt when a United flight with 263 people onboard experienced turbulence halfway through a 13-hour trip from Washington to Tokyo.
In May, 10 people suffered injuries, including broken bones, on a United flight that hit severe turbulence over the Atlantic Ocean on its way from London to Los Angeles. The Boeing 777 was diverted to Montreal.
Associated Press writers Judith Kohler, Thomas Peipert, Dan Elliott and Colleen Slevin in Denver; Joan Lowy in Washington; and Denise Petski in Los Angeles contributed to this report.