Five people were killed and more than 40 were injured after a driver in an SUV plowed through a Christmas parade in Waukesha, Wis., on Sunday, officials said — a violent end to the otherwise festive scene where children were dancing in the street and a marching band played “Jingle Bells.”

The toll of dead and injured could increase as more information is gathered, the Waukesha Police Department said early Monday.

Authorities have recovered the driver’s vehicle and have taken one person into custody, Waukesha Police Chief Dan Thompson said at a news conference Sunday evening. Thompson said the investigation was still “very fluid” and that it was “unknown at this time whether the incident has any nexus to terrorism.” He did not comment on a possible motive. The FBI said it was assisting local authorities in the investigation.

Waukesha Fire Chief Steven Howard said first responders activated their “mass casualty protocols” and took 23 people to hospitals, including 12 children. Additional people were transported to medical facilities by the police and family members, he said.

“We saw an SUV speeding down the parade route,” Angelito Tenorio, who is running as a Democrat for Wisconsin state treasurer, told The Washington Post on Monday. “We didn’t know if this was an accident or a deliberate attack.”

Tenorio, who attended the parade with his family and campaign manager, had been marching with the Waukesha County Democrats shortly before the incident. What came next was a “loud bang,” “deafening cries and screams” and a wave of “fear and agony,” said Tenorio, a West Allis alderman. The streets turned chaotic as parents rushed to protect their children and parade attendees fled the scene, leaving a trail of belongings behind them.

The parade — a highly anticipated event in Waukesha, about 20 miles west of Milwaukee — turned from a happy, bustling atmosphere to one of “absolute chaos,” he said.

“After the crowd had cleared out, that’s when I saw what looked like people who were laying on the ground, lifeless,” he continued.

Waukesha Mayor Shawn Reilly, who also participated in the parade, described a jubilant atmosphere that quickly turned nightmarish. “Today we experienced a horrible, senseless tragedy,” he said. “I walked in the parade at the beginning. I saw all the happy children sitting on the curb. I saw all the happy parents behind their children. I can still see the smiling faces.”

The vehicle broke through barricades about 4:40 p.m. local time, roughly 40 minutes after the parade began.

In video of the parade streamed by the city to its Facebook page, the SUV is seen speeding down the parade route seconds after a marching band playing “Jingle Bells” had passed. Onlookers screamed at the sight of the vehicle barreling down Main Street, whizzing past a Jeep that was outfitted in Christmas lights, as a police officer chased the SUV on foot.

After the parade carried on for a few minutes, emergency vehicles sped by, sirens and lights blaring, as a group of children dancing with snowflake props tried to carry on with their performance.

A police officer fired at the SUV in an attempt to stop it, said Thompson, the police chief. No bystanders were injured by the gunfire, he said, adding that authorities did not believe any shots were fired from the vehicle.

“We heard people screaming,” Zack Heisler, a Milwaukee resident at the parade with his family, told The Post. “It sounded like excitement, and the screaming sounded closer, then it sounded like terror. People sounded scared.”

Heisler said he saw a car “flying past us” and “people flying everywhere.”

When Angela O’Boyle got home from work, the parade was ongoing. She stepped out onto her balcony to record the festivities just below so she could share it with family who couldn’t be at the parade.

Eight seconds into a video she shared with The Post, a red SUV rams into a band playing just under O’Boyle’s view.

“It didn’t seem real. You’re watching it, but you’re not watching it happen,” O’Boyle said in an interview. “I was watching it through this lens.”

She continued to watch as the driver got to the end of the long block. Shrieks and gasps can be heard in the video, as parade-goers start to run toward those who had been hit.

Dan Schneiderman, owner of the local Vinyl Vault record store, said he was standing at the store window when it suddenly felt like things went into slow motion. He said he “heard the thud thud thud” of people being hit “and the car screaming past.”

He said he will not forget the sound of the car hitting people.

“I ran out the door, and it was mass chaos. There were people running eastbound up Main Street screaming,” Schneiderman told The Post. “I started grabbing people. It’s a small sidewalk. Herding as much people in as I could.”

Dozens huddled inside his tiny music store, he said. As they waited, there was silence.

“There was no conversation. Every single one of them had a look of fear on their face I’ll never forget,” he said. “That was more fear I’ve ever seen in my lifetime. The most scared I’ve ever seen of a human being.”

A red SUV ran through a Christmas parade in Waukesha, Wis., on Nov. 21, injuring more than 40 people, according to the city's police chief. (Bartolome Jesus via Storyful)

Kaylee Staral, an intern at the Milwaukee Journal Sentinel, attended the parade with her family members, who took their spots next to parents and children with candy bags and blankets. “It was supposed to be an exciting event,” Staral, 20, said in an interview with The Post. “A bunch of little kids were there. People were there to get in the holiday season.”

Minutes later, the SUV shot past Staral and her family, and they watched as it rammed into participants. She counted four people injured on the pavement in front of her. All around, people were screaming and crying as they rushed into stores for shelter and tried to help those injured.

“Everyone was just watching the parade go by and having a good time,” Staral said. “I don’t think anyone expected anything like this to happen.”

Corey Montiho, a Waukesha School District board member, was with his family at the parade, where his daughter’s dance team was performing. They were watching a high school marching band when the vehicle plowed through, hitting several of his daughter’s team members, he said. People scrambled to help, he said. “I saw bodies and kids and dads not breathing,” Montiho said. His daughter was not injured, but many of her teammates were in critical condition early Monday, he said.

Montiho said he had made eye contact with the man driving the SUV, describing him as “calm and composed.”

Children, some as young as 4 years old who were set to dance or walk in the parade, took shelter inside St. Matthias Episcopal Church on Main Street, where Pastor David Simmons, a Kentucky native who moved to Waukesha 23 years ago, said some waited hours to be reunited with their parents, who were waiting for them on the other side.

Simmons said he and others who were going in and out of the church to stay warm or use the toilets saw the SUV emerge from the right-hand side of the street and heard the driver “[honk] his horn really vociferously, which looked at least to us like he was trying to get people out of the way.”

“He could’ve been going down the middle of the road and he was not,” Simmons added. “As he swerved and headed downtown and picked up speed, he was heading down to the park, where the parade was more tightly packed. Most of us assumed that he would get down a block or two and then the police would pull him over onto another side road.”

“It didn’t seem like somebody was trying to cause a mass casualty incident; it felt like somebody was being [an] irresponsible, dangerous jerk.”

The episode shocked the community of more than 70,000 just days before Thanksgiving. The Archdiocese of Milwaukee said in a statement that one of its priests, as well as multiple Waukesha Catholic School students and members of the church, were among those injured.

The Milwaukee Dancing Grannies, which describes itself as a “group of grannies that meet once a week” to practice dance routines for parades, said its members were also injured. “Please keep the Grannies, all those injured, and all those who witnessed this horrible event in your thoughts and prayers,” the group said in a Facebook post.

Scott Walker, former governor of Wisconsin, said his mother attended the parade and watched the SUV drive past. She left before it collided with people, but people soon came running past her, Walker said on Twitter. “She said it felt like the images of people running in NYC on 9/11,” Walker said.

Waukesha is a tightknit city, said Simmons, the Episcopal priest, but one that has not escaped some of the debates dividing communities across the United States. In June, the Waukesha School District board voted to opt out of a federally funded program that would give free meals to all students regardless of family income. Although the board eventually reversed its decision, it led to acrimonious debates among parents and residents, Simmons recalled.

“In Waukesha, we sometimes fight about all sorts of stuff,” he said, “but I do believe that when we hit a situation like this, that we’re able to stand together and stand as a community, and that’s really what I’m expecting to happen over the next day or two.”

What happened “won’t erase those problems, but I do think that we’ll be able to come together to grieve,” Simmons added.

School was canceled Monday for students in the Waukesha School District, the superintendent said in a note, adding that counselors would be provided Monday at school buildings for students in need of support.

Gov. Tony Evers (D) said he and his wife were “praying for Waukesha tonight and all the kids, families and community members affected by this senseless act.”

Evers said he had ordered U.S. and Wisconsin flags to be flown at half-staff “as we continue to pray for the Waukesha community and the kids, loved ones, and neighbors whose lives were forever changed by an unthinkable tragedy last night.”

Alice Crites, Paulina Firozi, Mark Guarino, Rachel Pannett and Annabelle Timsit contributed to this report.