Video of police officers dragging a passenger from an overbooked United Airlines flight is sparking uproar on social media.

As the flight waited to depart from Chicago's O'Hare Airport, officers could be seen grabbing the screaming man from a window seat, pulling him across the armrest and dragging him down the aisle by his arms. The airline was trying to make room for four of its employees on the Sunday evening flight to Louisville, Kentucky.

Passenger Audra Bridges posted the video on Facebook. Her husband, Tyler Bridges, said United offered $US400 ($A534) and then $US800 vouchers and a hotel stay for volunteers to give up their seats. When no one volunteered, a United manager came on the plane and announced that passengers would be chosen at random.

When airline employees named four customers who had to leave the plane, three of them did so. The fourth person refused to move, and police were called, United spokesman Charlie Hobart said.

The passenger told the manager that he was a doctor who needed to see patients in the morning, Bridges said.

A few minutes later, the man who was removed from the plane returned, looking dazed and saying he had to get home, Bridges said. Officers followed him to the back of the plane. Another man travelling with high school students stood up at that point and said they were getting off the plane, Bridges said.

About half of the passengers followed before United told everyone to get off, he said.

The man who was originally dragged down the aisle was removed from the plane again, and United employees made an announcement saying they had to "tidy up" the aircraft, Bridges said.

After a three-hour delay the flight took off without the man aboard, Bridges said.

Airlines are allowed to sell more tickets than there are seats on the plane, and they routinely overbook flights because some people do not show up.