The Driving Home For Christmas singer, 66, suffered a stroke last year and was just nearing the end of a 37-venue tour.
Fans shared their shock as they watched the star fall to the ground and began “shaking on the floor”, they wrote online.
He reportedly was taken away in an ambulance.
Shocked fans took to social media to share what happened, with one writing: “I’m at the New Theatre Oxford. Moments after I took this photo Chris Rea collapsed on stage. Fell backwards after shaking and struggling to hold the microphone.”
“Hoping @chrisreamusic just over heated. Collapsed on stage at 9.30pm this evening in Oxford. Was such a great set too. #RoadSongsForLovers,” another wrote.
“Feeling devastated. While watching one of my guitar heroes, Chris Rea, play tonight, he just collapsed about an hour into his set. Ambulance took him away. Please pray that he is okay,” another wrote.
OK! Online have contacted a representative for Chris for updates on his condition.
Chris recently opened up to Gazette Live about his stroke last year, stating that when he battled pancreatic cancer in the early 2000s he was “still getting the affects” from years before.
“I just keep having the worst luck in the world,” he said. “I’m still getting the affects from 15 years ago – because I didn’t die!”
He admitted he gave up cigarettes following the stroke, adding: “I was on a LOT of cigarettes!
“I’ve sung my first song without a cigarette – that was very strange.
“I’m fine when I’m sitting down. I’ve just got a bit of balance that’s dodgy, in case someone thinks I’m drunk on stage.”
Saying two of his fingers were affected by the stroke, he added: “Music is a kind of therapy because you have to make yourself do it. I’m having to practise. There’s things I’ve never thought playing ever before.”