The 'R.I.P' singer was carried out of her make-up trailer during the beginning of shoot at Soho Beach House Hotel in the Florida resort at about 2.30pm.
A source told Gossip Extra that the ambulance had its lights flashing and the 22-year-old singer was photographed being put onto a stretcher.
She is believed to have been suffering from exhaustion and was taken to Mount Sinai Medical Centre in Miami Beach.
The blonde star has spent the weekend in the sun-kissed town modelling for Madonna and daughter Lourdes' junior clothing line, Material Girl.
Just hours before being rushed to hospital she had been tweeting her excitement about being included in MTV's Top Stars of 2013 list and also wished her brother Don Ora a happy 16th birthday.
She later tweeted: "@madonna @materialgirl #materialgirlmiami. Let's have this Miami..... let the fun begin...." Although it is not known if she posted the message after passing out.
Madonna previously said about the star: "Rita is a talented beauty but what really drew us to her is the confidence she oozes through her music and her unique sense of style.
"On stage or off, in photos or on the street - she's a magnet! This is what the Material Girl brand is all about!"
Rita first met the 53-year-old Queen of pop at the Sound for Change concert in London earlier this year.