A bomb threat closed a suspension bridge north of Detroit for several hours Sunday, officials said. The Mackinac Bridge Authority said on Twitter that the bridge was closed at 2:15 p.m. Sunday after law enforcement reported a bomb threat. After an "extensive search," nothing was found, the authority said. The bridge was reopened by about 5:10 p.m. local time, according to a post from a Mackinac County 911/ Emergency Management Twitter account connected to the Mackinac County website. Both Michigan State Police and the Mackinac City Police Department were continuing to investigate the incident. Mackinaw City police told 9&10News that a caller said that he had planted a bomb underneath the bridge. The caller said that he was in a car at a nearby gas station, though no car was ever found.