Dozens of people have been rescued from a FedEx depot in Michigan that had partially collapsed after a tornado.
The rare tornado hit the small town of Portage, eight miles (13km) south of Kalamazoo, on Tuesday evening.
Officials said all 50 people trapped inside escaped with no serious injuries.
Severe weather warnings are still in place from Ohio to Mississippi with a few tornadoes still expected.
Michigan's tornadoes damaged buildings and power lines in the region, and on Wednesday, more than 56 million people remained under threat in at least 18 states.
More than 30,000 people are still without electricity, according to the PowerOutages US website.
The severe weather marks the first-ever tornado emergency - the highest level - issued for Michigan from the National Weather Service (NWS).
Officials said up to 16 people suffered non-severe injuries after the tornadoes ripped through nearly 200 mobile homes in the area.
"We found homes in the roadway, we found homes in neighbours' homes. We found large trees in homes. We found many vehicles that had been smashed by large trees or homes," Kalamazoo County Sheriff Richard Fuller said on Tuesday.
He credited the low injury rate to people's awareness and readiness for the severe weather, as well as the swift and coordinated response by emergency crews.
The tornadoes also damaged the FedEx facility in Portage, Michigan. Officials said collapsed wires and debris had to be removed in order to reach those who were stuck inside.
All were safely rescued by early Wednesday, the Kalamazoo County Government said in a statement.
Late on Tuesday, FedEx said in its own statement that it is "grateful there were no serious injuries resulting from damage to our facility".
Over a dozen tornadoes were reported on Tuesday evening in Michigan, Indiana and Ohio. A few others were reported on Wednesday morning in Arizona and West Virginia.
Officials are bracing for a third day of "particularly dangerous" tornadoes on Wednesday, predicting threats of severe weather in an area stretching from Springfield, Missouri to Louisville and Nashville in the east.
In addition to severe storms and tornadoes, powerful wind is also expected for parts of Tennessee, stretching down to Dallas, Texas.
