At least five people are dead and more than 40 injured, many of them children, after an SUV sped through barricades and into a Christmas parade in the US state of Wisconsin.
Officials from the city of Waukesha confirmed the toll late on Sunday, while noting that it was still collecting information.
A "person of interest" was in custody, Waukesha Police Chief Dan Thompson said, but he gave no details about the person or any possible motive.
"What took place in Waukesha today is sickening, and I have every confidence that those responsible will be brought to justice," Attorney General Josh Kaul, the state's top law enforcement officer, tweeted.
The horror was recorded by the city's livestream and onlookers' mobile phones. One video shows the moment the SUV broke through the barricades and the sound of what appears to be several gunshots. Thompson said a Waukesha police officer fired his gun to try to stop the vehicle. No bystanders were injured by the gunfire, and Thompson said he did not know if the driver was struck by the officer's bullets.
Another video shows a young child dancing in the street as the SUV speeds by, just a few feet from her, before it hurtles into parade participants ahead.
One video, of dancers with pompoms, ends with a group of people tending to a girl on the ground.
The Milwaukee Dancing Grannies, who were also taking part in the parade, posted that "members of the group and volunteers were impacted and we are waiting for word on their conditions."
A Catholic priest, multiple parishioners and Waukesha Catholic schoolchildren were among those injured, the Archdiocese of Milwaukee spokeswoman Sandra Peterson said.
Chris Germain, co-owner of the Aspire Dance Centre studio, had about 70 people in the parade ranging from as young as 2 being pulled in wagons to age 18. Germain, whose own 3-year-old daughter was in the parade, said he was driving at the head of their entry when he saw a maroon SUV that "just blazed right past us." A police officer ran past in chase. Germain said he jumped out of his own SUV and gathered the girls who were with him to safety.
Then he walked forward to see the damage.
"There were small children laying all over the road, there were police officers and EMTs doing CPR on multiple members of the parade," he said.
The Waukesha school district cancelled Monday classes and said extra counsellors would be on hand for students and staff.
Governor Tony Evers said he and his wife, Kathy, were "praying for Waukesha tonight and all the kids, families, and community members affected by this senseless act."
Waukesha is a western suburb of Milwaukee, about 90 kilometres north of Kenosha, where Kyle Rittenhouse was acquitted on Friday of charges stemming from the shooting of three men during unrest in that city in August 2020.