Mr. Ayala said that people should call the authorities if they know someone who is missing.
The deaths in Madison County — including two children younger than 5 — occurred at different locations. Mr. Ayala did not disclose more details about the deaths because some victims’ families had yet to be notified.
Mr. Ayala estimated that 25 to 30 homes had been destroyed but said a fuller assessment would come in the morning.
The National Weather Service said that a preliminary examination of photos and videos from around Winterset, a city in Madison County, suggested damage from a tornado with wind speeds of more than 135 miles per hour.
The agency’s survey teams will further investigate the damage on Sunday, officials said.
Video posted on social media and recorded south of Winterset showed the aftermath of the severe weather: piles of debris, smoke and a car flipped upside down.
Officials in Lucas County did not release details about the death there, also because family members had not been notified. Another person was seriously injured, a few had minor injuries, and four to six homes in the rural area were “majorly impacted,” Mike Lamb, the emergency management coordinator for Lucas County, said late Saturday.