Driving Home for Christmas singer Chris Rea is in a "stable condition" after he collapsed on stage while performing in Oxford on Saturday.
South Central Ambulance Service said paramedics were alerted at 9.30pm to the incident at the New Theatre Oxford, with one audience member describing the performer "falling into a clump."
A spokeswoman for the ambulance service said: "We had an ambulance crew on scene and one patient has now been taken to hospital."
When asked about the condition of the person, she said they were "stable."
The incident comes after the songwriter suffered a stroke last year.
Darren Fewins, who had been watching the show with his wife, said the 66-year-old had been performing his set for 40 to 45 minutes before falling backwards.
He said: "He was standing by the microphone and he had the guitar in his hand and he kept shaking his left hand as if there was something not quite right with it.
"He walked forward to the microphone and he was trying to grab the microphone with his left hand, and it was swinging from side-to-side.
"I thought at first there was something wrong with it and he was trying to keep it steady. He then took three or four steps backwards.
"Then he just collapsed on the stage backwards. There was no one there to catch him; he just fell into a clump. He was on his back for about two minutes before they brought the curtain down and then that was it."
Mr Fewins said the singer "looked brilliant" before the dramatic end to the gig and said he had been getting the crowd to clap along to the music.
"He looked fit, he looked well. He was changing guitars every song and he just looked like someone who I have seen several times and was playing the best I have ever seen," the music fan said.
The shocked crowd was eventually told the show had ended as staff asked people to leave the venue.