Police are investigating after a shot was fired, and a woman ran onto a freeway and was fatally struck Monday evening near Luna Pier, Michigan.

Southbound Interstate 75 in that section of Monroe County was closed overnight but reported back open at 5:50 a.m. Tuesday as a result of the investigation, according to the Michigan Department of Transportation's traffic map. Motorists were urged to take alternate routes overnight.

According to Michigan State Police, a U.S. Customs and Border Patrol agent was on southbound I-75 at about 8:28 p.m. when he stopped to help the stranded female driver from Monroe. After getting her information and returning to his car, the agent heard a gunshot and saw someone running from the area into the woods.

The woman then got out of her car and attempted to run across the freeway when she was fatally struck. She was pronounced dead at the scene.

It is unknown if the person came from the vehicle or if he fired the shot. Investigators searched the area and did not find anyone.

Luna Pier is at Exit 6, about 10 miles south of Monroe.

An investigation is ongoing. Anyone with information on the incident is asked to contact the MSP Monroe Post at 734-242-3500.