Two vehicles collided on the bridge, one with two wheels and the other with the guardrail. This dramatic photo circulated on social media as well as in news reports.
The authorities did not provide any details.
According to social media posts, a caller from the bridge reported that a vehicle crossed the median at the bridge's south end. A second caller claimed it had struck another vehicle.
The Mackinac Bridge, or Mighty Mac, spans the Straits of Mackinac. It connects the Upper Peninsula and Lower Peninsulas. It is currently the fifth-longest suspension Bridge in the world.
Two vehicles have been lost from the Mighty Mac since its opening in 1957.
The first incident, in 1989, saw a woman die when her car fell over the railing. According to reports, the driver lost control and drove across the median crossing northbound lanes. She then hit a curb before plunging.
A man drove his car into the edge of the road in 1997 as a suicide attempt.