Two were taken to nearby trauma centers and three others were transported to local hospitals with non-life-threatening injuries, Miami-Dade Fire Rescue said. The injuries suffered by the sixth individual were not immediately made available.
The Federal Aviation Administration said in a statement a single-engine Cessna aircraft flying from Fort Lauderdale-Hollywood International Airport lost power and struck a vehicle on the bridge while landing.
Three people were on board the aircraft, the FAA said.
Video taken from the balcony of a nearby hotel by Miami resident Alex Huberman showed the small, wrecked plane on fire, with dark smoke rising from it.
Several feet away from the plane was a maroon-colored SUV, which appeared to have sustained extensive damage, the video shows, suggesting it may be the vehicle the plane struck when attempting to land.
Huberman said he saw at least two people get out of the plane, adding several people were put on stretchers by emergency personnel.
Chad Raney, who shot another video of the accident, told CNN he had a boat at a marina next to the bridge and heard an explosion.
He went up to see what happened and recorded the aftermath of the crash. His footage showed dark plumes of smoke rising above the aircraft.