A red sports utility vehicle ploughed into the crowd at a Christmas parade in the US state of Wisconsin on Sunday, leaving at least five people dead and more than 40 injured, police said.

The incident occurred around 4.39 p.m. local time (2139GMT) in Waukesha city. Footage on social media showed people panicking and some were seen lying on the ground.

"At this time, we can confirm that five people are deceased and over 40 are injured. However, these numbers may change as we collect additional information," the Waukesha Police Department said on Facebook.

The scene is "still fluid" and an investigation into the incident is ongoing, it further said.

A person of interest is in custody, the police added.

Waukesha Police Chief Dan Thompson earlier told a press conference that a police officer fired at the suspect's vehicle to stop it and no bystanders were injured as a result of the weapon discharge.

"We're no longer looking for the suspect vehicle," said Thompson. "The scene is safe and secure."

Speaking at the news conference, Waukesha Mayor Shawn Reilly called the incident a "horrible and senseless tragedy.”

"Today our community faced horror and tragedy in what should have been a community celebration. I'm deeply saddened to know that so many in our community went to a parade but ended up dealing with injury and heartache," he said.

"My heart goes out to all those affected by the senseless act. My heart goes out to those injured as well as to their families.”

*Ali Murat Alhas in Ankara contributed to the story.