Fifteen people have been killed in Iowa due as a result of severe weather conditions and thousands have been left homeless, Voorhees said.
Ten counties in Iowa are under evacuation orders and 83 others in the state have been declared disaster areas.
Two people were killed by floodwaters in Indiana and two delivery people drowned on Sunday when their car fell into a flooded creek, the National Weather Service said.
One other person was killed on Wednesday when a tornado tore through Chapman, a town in the state of Kansas.
The deaths come in the wake of a major tornado on May 25 and subsequent heavy rains.
Four boy scouts were killed on Wednesday when another tornado ripped through western Iowa.
Serious flooding has hit several contiguous states in the US including parts of South Dakota, Minnesota, Wisconsin, Nebraska, Illinois, Indiana, Kansas, Oklahoma and Arkansas.
At least 53 locations in those states were expected to see "major flooding" in the next two days, the National Weather Service said.