Sir Salman Rushdie is reportedly on a ventilator and may lose an eye after he was stabbed on stage in the US on Friday.

Rushdie's agent Andrew Wylie told the New York Times that the news was "not good," adding that Rushdie could not speak, while the nerves in his arm were severed in the attack and his liver was "stabbed and damaged".

The British author, who has lived under the shadow of a fatwa imposed 33 years ago, was appearing at a literary festival in western New York State when the assailant, dressed in black, ran at him from behind and attacked him.

Police confirmed the detention of Hadi Matar, 24, of Fairview, New Jersey, who they believed was acting alone, but said they had not yet established a motive. The alleged assailant's name is common among Shia Lebanese Muslims.

In a press conference held in Jamestown, New York, police officials alleged the suspect jumped on stage and stabbed the writer at least once in the neck and once in the abdomen.

Witnesses said Rushdie was stabbed “10 to 15 times” and crashed through a stage barrier. He lay in a pool of blood as members of the audience and a police officer tackled the knifeman.

New York State police said he had been flown to a local hospital by helicopter. He has been undergoing emergency surgery for several hours.

Kathy Hochul, the New York Governor, said Rushdie was “alive” and “getting the care he needs” in hospital. She called the attack “heartbreaking”, adding: “It was a police officer who stood up and saved his life and protected him.”

Rita Landman, an audience member, said she believed the author suffered numerous knife wounds, including one to the right side of his neck. She said: “People were saying: ‘He has a pulse, he has a pulse, he has a pulse.’”

Dr Martin Haskell, a physician who was among those who rushed to help, described Rushdie's wounds as "serious but recoverable."

Ralph Henry Reese, who was onstage with Rushdie to moderate the event and sustained an injury to his face during the attack, was released from a hospital on Friday. 

Prime Minister ‘appalled’ by attack

Boris Johnson said he was “appalled that Sir Salman Rushdie has been stabbed while exercising a right we should never cease to defend”, adding: “Right now, my thoughts are with his loved ones. We are all hoping he is ok.”

The attack happened shortly before noon as Rushdie was being introduced at the Chautauqua Institution for a discussion about the United States as a place of asylum for writers and artists in exile.

The centre is 55 miles southwest of Buffalo in a rural, quiet corner of New York State, and is known for its summertime lecture series. Rushdie had spoken at the event before.