After initially touching down as a weak tornado, the NWS said it quickly intensified into a destructive force.
A machine shop was swept from its foundation and destroyed, killing one man and injuring another person.
“At one homestead, a well built two-story house was completely swept from its foundation and decimated in a widespread and distant debris field," the NWS said in its report.
A couple taking shelter at the home was injured when a vehicle and other debris were thrown into the exposed basement..
Forecasters said the storm continued east across Southern Otter Tail County and may have produced one or more additional, but brief, tornadoes along its path.
The NWS said it was the first EF-4 tornado to hit Minnesota since 2010.
According to the National Severe Storms Laboratory, the most common and practical way to determine the strength of a tornado is estimating wind speeds by assessing the damage caused. The Enhanced-Fujita Scale (EF), used since 2007, is how the NWS rates tornadoes.
The Storm Prediction Center said EF-4 tornadoes are considered to be "violent," with winds between 166 and 200 mph. Twisters in this second-strongest category create "devastating" damage.
Ashby Mayor Tom Grover, who described the tornado as "pretty destructive," said three farmhouses were also hit, with one completely flattened.
An EF-4 tornado packing 175 mph winds in Tennessee left 18 people dead in March.
Another EF-4 in Mississippi that had peak winds of 170 mph traveled at least 67.7 miles, officials said.
More severe weather was reported across Minnesota on Saturday as a storm system pushed across the state.
There was one report of a tornado near Cormorant, Minn., but no reports of any significant damage or injuries, FOX9 reported.
Another round of severe weather is expected in the region on Monday.
Fox News' Barnini Chakraborty contributed to this report.