Update: 7:55 p.m.
Mackinac Bridge Authority administrator Bob Sweeney said the driver likely suffered a heart attack while driving south near mid-span of the five-mile-long bridge.
He missed one car but hit another going in the opposite direction. Two people in the car were taken to a local hospital, but Sweeney says their injuries were not believed to be life-threatening.
Identities haven't been released.
The Michigan State Police St. Ignace post received a call of a fatal crash on the Mackinac Bridge shortly before 2 p.m.
The crash happened when a semi truck traveling southbound crossed the center divider, struck a rail, avoided one car, hit the rail again, then hit an oncoming car, according to the Mackinac Bridge Authority. The semi travelled approximately a quarter mile after crossing the center line before hitting the car.
The Michigan State Police St. Ignace Post says that the driver of the semi died from what is believed to be a medical condition.
The Mackinac Bridge closed to traffic as the Michigan State Police worked the scene of the crash.
Traffic was last reported to be backed up a quarter mile on US-2, and it is believed to be about the same on the Mackinac City side of the bridge, according to the bridge authority.
The bridge reopened around 5:30 p.m. to both sides of the bridge.
Winds were minor at the time of the crash, according to authorities. Traffic was not being escorted across the bridge at the time of the incident.