Waukesha authorities confirmed the deaths in a statement late Sunday. Police said the numbers could change as many people transported themselves to hospitals.
No names or ages of the dead were immediately released, but Police Chief Dan Thompson earlier said that "some injured are children and are some fatalities as a result of this incident."
A person of interest was in custody and the suspected vehicle was recovered, but no details have been given on a possible motive.
A live video feed of the parade from the city of Waukesha showed the SUV breaking through barriers and speeding into the roadway where the parade was taking place.
Victims were transported to hospitals via ambulances, police officers and family members, according to officials.
An officer also discharged his weapon at the suspected vehicle to try and stop it but no bystanders were injured as a result, Thompson added.
Mayor Shawn Reilly tells WITI in Milwaukee that he does not believe there is any current danger to the public.
Police in Waukesha were urging people to avoid the downtown area Sunday night.
Angelito Tenorio, a West Allis alderman who is running for Wisconsin state treasurer, told the Milwaukee Journal Sentinel that he was watching the parade with his family when they saw the SUV come speeding into the area.
"Then we heard a loud bang, and just deafening cries and screams from people who are who are struck by the vehicle," Tenorio said. "And then, and then we saw people running away or stopping crying, and there, there are people on the ground who looked like they'd been hit by the vehicle."
Wisconsin Governor Tony Evers posted to Twitter saying: "Kathy and I are praying for Waukesha tonight and all the kids, families, and community members affected by this senseless act. I'm grateful for the first responders and folks who acted quickly to help, and we are in contact with local partners as we await more information."
Kathy and I are praying for Waukesha tonight and all the kids, families, and community members affected by this senseless act. I'm grateful for the first responders and folks who acted quickly to help, and we are in contact with local partners as we await more information.— Governor Tony Evers (@GovEvers) November 22, 2021
"The FBI Milwaukee field office is aware of the reporting of an incident in Waukesha. The local and state authorities are leading the response," an FBI spokesperson said.
An investigation is ongoing.