A United Airlines flight travelling from Vancouver to Chicago Monday afternoon had a near-collision with a glider over Rockford, Ill., U.S. Federal Aviation Agency said.

The pilot of United Flight 246 reported seeing a glider while flying near Rockford, the FAA said in an emailed statement. The airliner was approaching Chicago's O'Hare International Airport, a passenger said.

The Boeing 737 quickly climbed 122 metres to avoid a collision.

Callum Snape, a passenger on the flight, said the sudden manoeuvre was felt by all on board.

Passenger: 'All of a sudden the right wing just completely dropped'0:26

"All of a sudden, the right wing just completely dropped on the plane, and we did a really sharp turn right," he said. "No one screamed, but it was enough that many people grabbed their seats and their armrests.

"I couldn't see what was happening, but I knew that it was out of the ordinary."

The FAA said it will investigate.