New video recorded on a United Airlines aircraft shows the moments that led to a passenger being violently dragged from the flight.

The footage, captured by a passenger directly behind Dr David Dao, shows the Kentucky physician telling police he would rather go to jail than get off the plane, saying "you can drag me".

Earlier footage of Dao being dragged bloodied and screaming from the plane - scheduled to travel from Chicago to louisville, Kentucky - has made global headlines, earned the US carrier international condemnation and wiped a reported $1.3 billion from the company's value.

But video showing what led to the shocking act adds a surprising twist to the scandalous story.

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The clip, recorded by a woman sitting behind Dao, shows him talking on the phone while being asked to leave the aircraft by police.

He refuses, saying: "I won't go. I'm a physician, have to work tomorrow at 8 o'clock."

Dao is heard to say he will "make a lawsuit against United Airlines" and adamantly refuses to give up his seat.

A police officer says to Dao: "I have to drag you. You know how this is going to end up happening, right?"

A clearly angry Dao says the officer can drag him from the flight, and that he'd rather go to jail.

"You can drag me then, I don't go. I'm staying. You'll have to drag me," he said.

While the officer explains to Dao that not co-operating will make things "a lot harder for you", Dao interjects saying "I'd rather go to jail".

Confused, the cop questions Dao, seeking to clarify what he has said.

"You'd rather go to jail than just get off the plane?" he asks.

"Yeah," Dao is heard to reply.

Before the clip cuts out Dao is heard complaining that he has travelled "almost 24 hours" coming from LA, and protests further.

Dao is then dragged from his seat by police officers, sustaining injuries to his face.

The Elizabethtown man has hired a legal team and a lawsuit against United Airlines is expected.

After drawing criticism by claiming the passenger was "disruptive and belligerent", United chief executive Oscar Munoz later issued Dao a grovelling apology.

The embattled CEO has appeared on US TV overnight in full damage control.

"You saw us at a bad moment and it can never and will never happen again on a United Airlines flight and that's my promise," Munoz told Good Morning America.

Asked what he thought when he first saw the footage, he said: "The word shame comes to mind".

"That is not who are family at United is."

Munoz said the company would no longer use law enforcement officers to remove passengers from overbooked flights.