Patti Smith collapsed on stage in Brazil mid-performance -- and she later rolled back out in a wheelchair to let the crowd know she had to cut the rest of the show short.

The 78-year-old music legend experienced the health scare 30 minutes into her performance at Sao Paulo's Cultura Artística Theater with the Berlin-based Soundwalk Collective group... and according to local news outlet, Folha de S.Paulo, it happened while she was reading a statement about climate change.

Patti was taken backstage, but later returned in a wheelchair to apologize ... saying, "Unfortunately, I got sick, and the doctor said I can’t finish. So we’ll have to figure something out. And I feel very badly."

Soundwalk Collective shared on their IG Story that Patti had been battling severe migraines recently and started feeling dizzy on stage during her performance -- but was now being cared for by the "best doctors in the most loving way."

The group assured fans that Patti was A-OK and would be back onstage tonight.