AT least some people were killed when a sports utility vehicle sped through a Christmas parade in Waukesha, Wisconsin, on Sunday, bowling over at least 20 people including several youngsters waving pompoms and a group of "Dancing Grannies".

Waukesha Police Chief Dan Thompson said a person of interest was in custody and the suspect vehicle had been recovered after the incident in Waukesha, about 20 miles (32 km) west of Milwaukee.

"The vehicle struck more than 20 individuals. Some of the individuals were children and there are some fatalities as a result of this incident," Thompson told reporters.

Asked about the fatalities, Thompson said: "I don't have an exact number at this time."

It was not known whether the incident was related to terrorism, he added.

A shelter-in-place order had been lifted, police said.

A video posted online of the incident showed a red SUV plowing through the parade, appearing to run over more than a dozen people.

In a second video, police appeared to open fire on the vehicle as it crashed through street barriers.

Thompson said an officer fired shots at the vehicle and no bystanders were injured.

Belen Santamaria, her husband, and their three-year old daughter were planning to join the parade with their Catholic Church. But Santamaria, a 39-year old Mexican factory worker, woke up on Sunday with a backache, so the family watched the procession from the sidewalk instead.

"The SUV came by at full speed," said Santamaria. "Then I started to hear people screaming."

She hid in a restaurant with their daughter while her husband, 39-year old delivery worker Jesus Ochoa, ran ahead to try to help injured people. He said he heard through other members of their church that roughly 10 members, mostly Latinos and both adults and children, are injured.

"I was going to be there, walking," Santamaria said. "The SUV would have hit us too."

A woman told Milwaukee's Fox6 TV station that the SUV hit a dance team of girls between 9 and 15 years old. She said the immediate reaction was silence, followed by screaming, running and checking on those injured, Fox6 reported.

One witness said the driver hit the "Dancing Grannies" and at least one person flipped over the hood of the SUV, according to Milwaukee's WISN-TV, an ABC affiliate.

"Members of the group and volunteers were impacted and we are waiting for word on their conditions," the Milwaukee Dancing Grannies said on their Facebook page. "Please keep the Grannies, all those injured, and all those who witnessed this horrible event in your thoughts and prayers."

The local CBS affiliate later showed a picture on Twitter of what appeared to be the red SUV involved with its hood crumpled and front fender hanging off, parked in a driveway.

Another witness estimated the SUV was going about 40 mph (64 kph) when it hit the crowd parading down the street, the TV station said.

Photos and videos of Waukesha circulating on Twitter showed police cars and ambulances crowding a street decked out with Christmas lights in the aftermath of the incident. People bundled up against the cold huddled on sidewalks as dusk fell.

Some of the injured were taken to the hospital by ambulance, others by police and still more by family and friends, Thompson said.

The incident occurred around 4:39 p.m. (2239 GMT), police said.

"As we were walking back in between the buildings ... we saw an SUV cross over, just put the pedal to the metal and just zooming full speed along the parade route. And then we heard a loud bang, and just deafening cries and screams from people who are struck by the vehicle," Angelito Tenorio, an alderman in nearby West Allis, told the Milwaukee Journal Sentinel.

In 2015, four people were killed and 46 injured in Stillwater, Oklahoma when a woman drove into a crowd watching the homecoming parade for a football team.

A truck was deliberately driven into a Christmas market in Berlin, Germany in 2016, killing 12 people in an attack linked to Islamic State.