Soon after the National Weather Service issued tornado warnings for the southern part of the state on Friday, videos on social media claiming to be from the towns of Three Rivers and Union City showed massive whirlwinds tearing roofs off buildings and lifting debris into the air.
Video showed smashed buildings and cars, and poles, trees and road signs that had been blown over.
Three fatalities and a dozen injuries were reported in Branch County, where Union City is located, the county's sheriff's office said.
One person was killed and several injured in Cass County, according to local authorities.
"Multiple large structures - including homes and pole barns - sustained damage ranging from major structural impacts to complete destruction," according to a statement on a website for Cass County.
Power outages had affected hundreds of people, local officials said.
"We have multiple utility poles down, transformers damaged, and long stretches of power lines on the ground. The north side of Union Lake sustained some of the most severe damage, with roughly two miles of line brought down in that area alone," according to a posting on Union City's official Facebook page that said restoration might take several days.
Michigan Governor Gretchen Whitmer said she activated an emergency operations centre to monitor the situation.
"The state is ready to fulfil any resource requests that may arise. We've yet to receive any just yet. It's sounding like the local response is and has been able to address what's been a very devastating afternoon and evening in southwest Michigan," Clayton Cummins, a spokesperson for Michigan emergency services and police, told Reuters.
