CAR IN MOTION. INCIDENT HAPPENED AT MARKER 173 NORTHPORT FL FUMES WERE DETECTED WHILE DRIVING AS I LOOKED OVER THERE APPEARED TO BE SMOKE ON THE FLOOR OF THE FRONT PASSENGER SIDE. I NOTICED THE PASSENGER SEAT WAS WARM IN ONE SPOT SO I MOVED MY PURSE. MY PURSE WAS COMPLETELY MELTED AS I PICKED IT UP SMOKE CAME BILLOWING OUT FROM THE SEAT. I WAS INHALING SOME SORT OF TERRIBLE SMELLING SMOKE. I OPENED WINDOWS SO I COULD BREATHE. THE SMOKE WAS GETTING THICKER. COULD NOT SEE FROM WINDOWS TO GET OVER TO RIGHT SIDE OF ROAD. ALSO AS DRIVING THE ODOMETER AND SPEEDOMETER NEEDLES WERE GOING BACK AND FORTH BUT I WAS DRIVING NORMALLY. I PULLED OVER SHUT CAR OFF. CAR SEAT CONTINUED TO BURN AND SMOKE. CALLED 911 AND FIRE DEPARTMENT HAD TO CUT BATTERY TERMINAL AND SPRAY CAR TO PUT FIRE OUT. HUGE HOLE IN SEAT WHERE FIRE WAS. SEAT WARMERS WERE NOT ON. THERE WERE NO PASSENGERS JUST MYSELF. IT IS UNKNOWN AS TO WHAT CAUSED THIS TO HAPPEN.