Residents fled rising waters from the Wild Rice River after 10 inches of rain fell in an area declared a flooding disaster just a week ago.
Roads were washed out and crops submerged in Mahnomen and Norman counties.
Gov. Jesse Ventura activated 70 members of the National Guard to help. The Mahnomen high school was turned into an emergency shelter.
Downriver from Mahnomen, guardsmen were working to shore up a permanent levee in Ada.
Time was limited as residents sandbagged before the floodwaters streamed into town, said Kevin Ruud, Norman County emergency director.
President Bush on June 14 declared a disaster area in 13 northwestern Minnesota counties because of flooding.