(CNN) -- The National Transportation Safety Board is investigating what happened during a United Airlines flight this week that led to 21 people being taken to hospitals.
United Airlines Flight 967 was en route from Washington Dulles International Airport to Los Angeles International Airport Tuesday night when it encountered severe turbulence over Missouri.
The Boeing 777 was diverted to Denver, Colorado, and landed about 7:30 p.m.
Twenty-one people were transported to hospitals, said Scott Bookman, chief paramedic of Denver Health. The Denver Fire Department earlier said that one person was seriously injured. Bookman did not comment on specific injuries.
"It's really unusual to see this many patients from a single episode of turbulence," he said.
Most of the injuries included moderate head, neck and back injuries, according to the chief paramedic.
"It seems like they got jostled around pretty good," he said.
The federal safety board said 17 passengers and four flight attendants reported injuries.
United said the plane had 255 passengers and a 10-member crew.