Updated 8.36am

United Airlines is facing a public relations disaster after footage of a passenger being forcibly dragged off an overbooked plane outraged social media users yesterday. 

The unidentified man, reportedly a doctor, screamed as a plainclothes officer yanked him from his seat and then dragged him down the plane aisle by his arms. Uniformed officers followed close behind as other passengers gasped and yelled in shock at the disturbing scene. 

A few minutes later, the man - bloodied and looking dishevelled - reappeared on the plane, repeating "I have to go home, I have to go home" as he jogged towards the rear of the plane. He eventually collapsed and was taken off the plane in a stretcher, the New York Times reported.

An airline spokesman said crew had asked the man to leave the plane "multiple times" and called police when he refused to comply. 

Passengers said the airline informed passengers that the plane was overbooked as they began boarding, and offered any passenger willing to give up their seat $400 in vouchers. 

An airline crew member then told the already-seated passengers that four more people needed to get off the flight and upped the voucher compensation to $800. When nobody came forward, crew selected four passengers to leave, including the man forcibly dragged off. 

'JUST KILL ME'

Multiple passengers shot video of the incident and posted it to Facebook and Twitter, and the footage quickly went viral.

The incident was one of the top-trending topics on Twitter as users took to the website to express their anger toward the airline.

Passenger Tyler Bridges said the man told United staff that he was a doctor and had to return home to his patients.

The airline said it had asked for volunteers to leave because additional flight crew needed to get to Louisville.

Many social media users criticised United for how it handled the situation.

"Apologize for saying you 'had to' do this. There were other options and you know it," user @TessaDare wrote in a series of posts retweeted thousands of times. "Apologize for creating and allowing a corporate culture that says it's okay to treat passengers with such disregard and disdain."

In 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 man's seat and snatch him from his chair.

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."

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

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

"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.

As outrage over the incident ballooned, United Airlines' CEO apologised for the "upsetting event" and said the company would be reaching out to the passenger to "further address and resolve this situation."

This is the second public relations meltdown United Airlines has had in less than a month. Just two weeks ago, the airline's decision to kick two young women off a plane because they were wearing leggings made headlines across the world.