The tornado warning is in effect until 6:30 p.m. Friday.
"Sirens have been activated through the center part of the county," said Sanilac County Emergency Manager Todd Hillman.
Hillman said no damage had been reported in the county. He was in Sandusky.
Sanilac County Sheriff Garry Biniecki also said sirens were sounding in the county.
Wayne County is under a flood advisory until 6 p.m.. Friday and Monroe County is under a severe thunderstorm watch until 10 p.m. Friday.
Check JustWeather.com for the latest severe weather alerts.