The man accused of driving his vehicle into a traditional Christmas parade near Milwaukee has been charged with murder, as the death toll rose to six.

The number of people killed in the incident increased after prosecutors reported the death of an eight-year-old boy.

Darrell Brooks, 39, appeared in Waukesha County Circuit Court and the court commissioner set bail at $US5 million.

Authorities said Brooks deliberately drove an SUV through police barricades on Sunday and through the annual parade in the city of Waukesha, about 32km west of Milwaukee.

Brooks was on Tuesday charged with five counts of first-degree intentional homicide, according to prosecutors.

The charges were set before the death of the eight-year-old was disclosed. Prosecutors said more charges were pending.

In addition to those killed, more than 60 people were injured.

Brooks, a Milwaukee resident, was arrested near the scene of the carnage on Sunday.

Police have ruled out terrorism as a motive and said Brooks acted alone.

The victims killed ranged in age from eight to 81, and included some members of the popular Milwaukee Dancing Grannies parade group.

The injured included at least 18 children, who suffered facial abrasions, broken bones and serious head injuries and were taken to Wisconsin Children’s hospital in Milwaukee.

The incident drew the attention of President Joe Biden, who called the attack “horrific” and Pope Francis.

The Vatican sent a condolence message to the Roman Catholic bishop of Milwaukee on Tuesday.

Video of the incident posted on social media showed a red SUV racing alongside the parade route and then into the procession, appearing to run over more than a dozen people before bystanders raced to help.

“I saw children who were run over,” Brian Hoffman, 33, a Waukesha resident, recounted on Monday.

“I am still totally shocked.”