At least 30 people were injured,one of them seriously,when a United Airlines plane flying from Washington DC to Los Angeles encountered severe turbulence,authorities said on Wednesday. The Boeing 777 plane with 255 passengers and 10 crew members aboard went though heavy turbulence while flying over Kansas and had to be diverted to Denver International Airport,where it landed at around 7:45 p.m. (local time) yesterday. "It was just a huge up and down," passenger Kaoma Bechaz told the Denver Post. She said the head of a woman sitting next to her slammed into 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. Twenty-six passengers and four crew members were injured,Federal Aviation Administration (FAA) spokesman Ian Gregor was quoted by media reports as saying. Eric Tade,Denver Fire Department spokesman,said one injury was serious but that most of the injuries were bruises,strains and sprains,the Post reported. A special United flight later took many passengers from the flight to Los Angeles. FAA spokesman Mike Fergus said the pilot reported "moderate to severe turbulence" to controllers. The plane was flying at 34,000 feet when the pilot asked for permission to be diverted to Denver. The seatbelt sign was on when the plane struck the turbulence,but not all passengers were strapped in,media reported. "For those couple of seconds I just saw people fly up in front of me and actually the lady sitting beside me,she flew up too. She hit the ceiling and landed on my lap," passenger Bryan Liu told a television channel. The National Transportation Safety Board is investigating the incident,media reports said. In February,about 20 people were injured when a United flight experienced turbulence during a 13-hour journey from Washington,DC,to Tokyo.