A structure fire in Port Huron called officials from Port Huron and Marysville at about 4:15 p.m. yesterday. Upon arrival rescue crews found heavy smoke coming from a rear apartment on the first floor of a home in the 900 block of St. Clair Street in Port Huron. Crews knocked down the fire and searched the home for occupants. The home was empty and the occupants arrived shortly afterward. Reports say four Port Huron engines responded to the fire and one engine was requested from Marysville for mutual aid. The cause of the fire continues to be under investigation.