The incident occurred at around 4:39 pm (22:39 GMT) on Sunday in the city of Waukesha, about 32 kilometres (20 miles) west of Milwaukee.
Waukesha Police Chief Dan Thompson said a person of interest was in custody and the suspect vehicle had been recovered, Aljazeera reported.
“A red SUV drove into our Christmas parade that we were held downtown. More than 20 individuals were injured as a result of this incident,” Thompson told reporters.
“Some of the individuals were children and there are some fatalities as a result of this incident.”
Asked about the deaths, Thompson said, “I don’t have an exact number at this time.”
It was not known whether the incident was related to terrorism, but an earlier shelter-in-place order in the town of around 72,000 had been lifted, he added.
RHM/PR