A United Airlines jet had to be diverted yesterday after 26 passengers and four crew were injured – one critically – when the plane hit severe turbulence.

The United Flight 967, which had taken off from Washington D.C. and was bound for Los Angeles, hit a huge pocket of turbulence in the skies over Kansas.

The turbulence, described as a “huge up and down”, threw one passenger flying into the ceiling, and another into the side of the cabin so violently that she left a crack above the window, passengers said.

A number of other passengers were badly bruised and left with whiplash, and the place was diverted to Denver International Airport so that the injured could be given emergency treatment.

The U.S. Federal Administrative Service confirmed that 26 passengers and four crew members were injured. Spokesman Ian Gregor one person was critically hurt, but he released no further details.

He added that inspectors found “no obvious damage” to the diverted plane’s exterior, and found nothing wrong during a preliminary look at the plane’s interior.

However the FAA and the National Transportation Safety Board will be looking more closely.

Flight 967 was flying over Kansas at an altitude of about 34,000ft when it hit the heavy turbulence. It was carrying 255 passengers and ten crew members.

One passenger Kaoma Bechaz, a 19-year-old Australian, described the turbulence as “just one huge up and down” to the Denver Post newspaper.

She also saw the head of the woman sitting next to her hit 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. But Bechaz said she wasn’t thrown around because her seat belt was tight.

United was working to find flights for the uninjured passengers last night. Airline spokesman Michael Trevino told the Denver Post that a special United flight took off for Los Angeles at 9:30pm carrying many passengers from the diverted plane.

Last night’s turbulence incident was the third this year for United. In February, about 20 people were injured when a plane encountered heavy turbulence midway through a 13-hour trip from Washington, D.C., 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.