The tornadoes hit Marshalltown, Pella and Bondurant as surprised residents ran for cover. The storms injured 10 people in Marshalltown and seven at a factory near Pella, but no deaths were reported.
Marshalltown , a city of 27,000 people about 50 miles northeast of Des Moines, appeared to have been hit the hardest. Brick walls collapsed in the streets, roofs were blown off buildings and the cupola of the historic courthouse tumbled 175 feet to the ground.
The only hospital in Marshalltown was damaged, spokeswoman Amy Varcoe said. All 40 of the patients at UnityPoint Health were being transferred to the health system's larger hospital in Waterloo as well as one in Grundy Centre, she said.
The emergency room in the smaller Marshalltown hospital remained open to treat patients injured in the storm, Varcoe said. Ten people hurt in the storm had been treated, she said. She did not know how serious those patients' injuries were.
Additional funnels were reported as the storm moved east of Des Moines past Altoona, Prairie City and Colfax.
National Weather Service meteorologist Rod Donavon said two primary storms spawned the series of damaging tornadoes. One developed in the Marshalltown area, causing damage there, while the other started east of Des Moines and traveled through Bondurant and into Pella.
The exact number of tornadoes and their strength will be determined later.
