Doctor dragged bleeding, screaming from overbooked flight in front of horrified passengers.

Passengers travelling on a United Airlines flight from Chicago to Louisville, Kentucky, looked on in horror as a man was dragged from his seat when the flight was overbooked.

The man – which some passengers posting on social media reported was a doctor – was forcibly removed from his seat by police, with video showing he suffered an injury to his mouth.

"This is wrong. Oh my God, look at what you did to him," one passenger can be heard screaming in video posted online of the incident.

United Airlines confirmed to WHAS11 that the flight was overbooked, and after no volunteers offered to give up their seats, passengers were randomly selected to be removed from the flight.

When the man was told he had been selected to be removed from the plane, he refused, explaining he had to get home to see patients at a hospital the next morning.

"When we didn't get the number of volunteers we needed then we had to follow Department of Transportation procedures and ask that customers, four of them, exit the aircraft," United spokesman Charlie Hobart told PEOPLE when asked about the incident.

"One customer refused to do that after we had explained the situation and apologised and let that customer know what we were gonna do on his behalf to get that customer to where he needed to be.

United CEO response to United Express Flight 3411. pic.twitter.com/rF5gNIvVd0

— United (@united) April 10, 2017

"He still refused, at which point we had to involve the Chicago Police Department."

Passengers were first offered $400 and a hotel stay to give up their seats on the flight to standby United employees who needed to be in Louisville, Kentucky, for a flight.

When no-one volunteered, the offer was increased to $800, before passengers were randomly selected to give up their seats.

Several witnesses say the man was "tossed against a metal armrest" before he was pulled from his seat and "dragged down the aisle as he screamed".

One passenger told the Courier-Journal that everyone on board was "shocked and appalled" at the way the man was treated.

"There were several children on the flight as well that were very upset," Audra Bridges said.

Audra's video of the incident, posted on Facebook, has now been viewed more than 1.7 million times.

"We are all shaky and so disgusted," she captioned the clip.

NJ.com reports the man was eventually allowed to re-board the plane, but seemed "bloodied and disoriented" when he returned.

The flight then took off, two hours behind schedule.