6 p.m. update
In a release, the United States Coast Guard confirmed that in addition to vehicles being unable to cross the bridge, commercial vessels in the area were instructed to anchor until the situation was resolved.
5:10 p.m. update
The Mackinac Bridge Authority has been given clearance and the bridge is now reopened.
5 p.m. update
The latest from the Mackinac Bridge Authority, in a social media post, the MBC confirmed that the bridge was closed at 2:15 p.m. when law enforcement notified the MBA of a bomb threat.
"After an extensive search, nothing has been found," the post said. "They are completing one more sweep and hope to re-open the bridge. MSP (Michigan State Police) and Mackinaw City police are investigating."
Original story
The Mackinac Bridge was closed shortly before 3 p.m. Sunday afternoon.
Details on why the bridge was closed are limited at this time, but media reports say that it was shut down due to a bomb threat.
TV6 in Negaunee, Mich. reported the closure was due to the threat, citing Michigan State Police.
Details on the length of the closure are not known at this time.