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An aviation security officer who dragged a passenger off of an overbooked United Airlines flight to make room for employees has been placed on leave, Chicago authorities said on Monday.

The officer - one of three involved in the Sunday night incident - did not follow protocol, according to a statement from the Chicago Department of Aviation, and as a result "has been placed on leave effective today pending a thorough review of the situation."

"The actions of the aviation security officer are obviously not condoned by the Department," the statement said.

The incident was one of the top-trending topics on Twitter as users took to the website to express their anger over the forceful removal of the passenger from United Flight 3411 as it was about to take off from Chicago to Louisville, Kentucky, on Sunday.

Video of the incident posted to Twitter account @Tyler_Bridges shows three security officers huddling over the seated passenger, who appears to be an older Asian man, before dragging him on the floor.

A passenger who was removed from a United Airlines flight in Chicago Credit: Audra D Bridges via AP

According to witnesses the man, one of four passengers randomly selected by United to leave the overbooked flight, protested that he was a doctor who needed to see patients in the morning, and that he was calling his lawyer.

One woman could be heard screaming: "Please, my God. What are you doing? No. This is wrong. Oh my God. Look at what you did to him. You busted his lip."

United had initially asked for four volunteers to deplane and get a flight the next day in return for $800 and night in a hotel, but there were no volunteers.

It then selected four people randomly using a computer and asked them to get off. Three did, but the man refused.

Officers from Chicago's aviation department police force then boarded the plane. Mr Bridges, a passenger, said the man's face was bloodied.

He said: "Everyone was shocked and appalled. There were several children on the flight as well that were very upset."

In Mr Bridges' video, a woman asks: "Can't they rent a car for the pilots and have them drive?" Two uniformed men then reach into the doctor's seat and yank him from his chair.

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Credit: Twitter

Fellow passenger Jayse D Anspach, who goes by @JayseDavid on Twitter, wrote: "No one volunteered (to leave), so @United decided to choose for us. They chose an Asian doctor and his wife."

While airport security staff were ejecting him, Mr Anspach wrote, his face was slammed against an arm rest, causing his mouth to bleed.

"It looked like he was knocked out, because he went limp and quiet," Mr Anspach wrote, "and they dragged him out of the plane like a rag doll."

Mr Bridge's video shows the passenger screaming as officers yank him from his seat. He is then seen being dragged down the aisle on his back by his hands, body limp, glasses askew and shirt pulled up above his navel.

Another video shows him, still disheveled from the altercation, returning to the cabin, running to the back of the plane and repeating: "I have to go home."

A spokesman for United initially said: "We followed the right procedures. That plane had to depart."

Oscar Munoz, CEO of United Airlines' parent company, apologised first in a written statement and then in a letter to employees on Monday evening.

Mr Munoz said he was "upset to see and hear about what happened" at O'Hare. He added, however, that the man dragged off the plane had ignored requests by crew members to leave and became "disruptive and belligerent," making it necessary to call airport police.

"Our employees followed established procedures for dealing with situations like this," Mr Munoz told employees. "While I deeply regret this situation arose, I also emphatically stand behind all of you, and I want to commend you for continuing to go above and beyond to ensure we fly right."

United Airlines CEO Oscar Munoz Credit: AP

Mr Munoz said that the airline might learn from the experience, and it was continuing to look into the incident.

The flight was operated for United by Republic Airline, which United hires to fly United Express flights. Mr Munoz said four Republic employees approached United's gate agents after the plane was fully loaded and said they needed to board. He said the airline asked for volunteers to give up their seats, and then moved to involuntary bumping, offering up to $1,000 in compensation.

Earlier on Monday Mr Munoz had said in a statement: "This is an upsetting event to all of us here at United. I apologise for having to re-accommodate these customers. Our team is moving with a sense of urgency to conduct our own detailed review of what happened."

He said the airline was also attempting to speak to the passenger directly to "resolve this situation".

Much of the uproar on social media surrounded the appropriateness of removing a paying customer in order to accommodate airline staff.

United CEO response to United Express Flight 3411. pic.twitter.com/rF5gNIvVd0 — United (@united) 10 April 2017

"They bloodied a senior citizen & dragged him off the plane so THEIR OWN STAFF could take his seat," one Twitter user wrote.

Other social media users questioned whether the man would have been removed as forcefully had he not been Asian.

Late last month, two teenage girls were denied boarding on a United flight from Denver to Minneapolis because they were wearing leggings.

United insisted they were simply enforcing an existing policy on dress codes for people, such as the girls, travelling on “buddy passes” – discounted travel for friends and family of employees.