The passenger who was forcefully dragged from his seat on an overbooked United Airlines flight has spoken from hospital, saying "everything was injured".

Dr David Dao, 69, told Kentucky TV station WLKY he "was not doing well", after being dragged bloodied and apparently unconscious along the central aisle by airline staff.

The family's lawyer Stephen Goland said his family was only focused on "Dr Dao's medical care and treatment".

"The family of Dr Dao wants the world to know that they are very appreciative of the outpouring of prayers, concern and support they have received," he said.

The United Airlines chief executive has apologised for the "truly horrific event" which occurred on United flight 3411 from Chicago, Illinois to Louisville, Kentucky, causing the company major turbulence after going viral on social media.

The airline's tagline is 'fly the friendly skies', but it has had a less-than-friendly reception from the public and from the sharemarket, losing around US$1 billion in value since the violent encounter.

The crew say they weret rying to make room for four employees of a partner airline, and had offered money to passengers willing to give up their seats.

"[The incident] has elicited many responses from all of us: outrage, anger, disappointment. I share all of those sentiments, and one above all: my deepest apologies for what happened," says United chief executive Oscar Munoz.



"Like you, I continue to be disturbed by what happened on this flight and I deeply apologize to the customer forcibly removed and to all the customers aboard. No one should ever be mistreated this way."

He says the company takes full responsibility and "will work to make it right".

In what may be a reaction to criticism the airline reacted too slowly, Mr Munoz says "it's never too late to do the right thing".

The company says it will now conduct a thorough review of crew movement, how they incentivise people to give up their seats and how the airline deals with overbooked flights.

It seemed a marked contrast to Mr Munoz's initial response in a staff email where he defended his employees.

He stated the passenger had been "disruptive and belligerent" and refused to voluntarily leave the plane, with staff "left with no choice but to call Chicago aviation security officers to assist in removing the customer from the flight".

The Chicago Department of Aviation said one of the three security officers involved has been placed on leave, and that his actions were "obviously not condoned by the department".

A review is underway by the department, along with a separate investigation by the US Department of Transportation, which is reviewing whether United complied with rules on overbooking.

Dr Dao's sordid past

The father-of-five trained at a Vietnamese medical school before moving to the US. He'd been living in Kentucky for around 20 years.

He was convicted on multiple charges of obtaining drugs by fraud in 2004 and was placed on five years' probation, Louisville's Courier-Journal reports.

The New York Post reports the Kentucky medical licensing board investigated Dr Dao after he was arrested and found he'd become sexually attracted to a male patient.

They began a relationship and would meet for sex in motel rooms where he'd trade drugs for sexual favours.

Dr Dao later hired the man as his office manager, but he quit after Dr Dao made "inappropriate" comments.

Social media backlash

Chinese internet users are now calling for a boycott of the airline.

Posts from official media accounts and private citizens were quickly seen trending on platforms including Sina Weibo, a Chinese version of Twitter, and on messaging platform WeChat, which has more than 800 million users worldwide.

Shenzhen Airlines set up an online poll of Weibo users' seeking their views on the scandal.

Many Weibo users said the move was insulting and disrespectful, arguing United Airlines deliberately targeted an Asian man because Asians were stereotyped as timid and unlikely to stand up for their rights.