At least 18 children are hospitalized after an SUV barrels into the Waukesha Christmas parade

It took just seconds for a family-friendly event to devolve into a scene of carnage and confusion.

in Wisconsin on Sunday, killing at least five people and injuring more than 40 others, officials said.

At least 18 children remain hospitalized Monday after the Waukesha Christmas parade, said Children's Wisconsin, a pediatric hospital in nearby Milwaukee.

The numbers of those killed and injured "may change as we collect additional information. Many people have self-transported to area hospitals," the city of Waukesha .

There are indications the driver was fleeing another incident when he drove into the parade route, according to multiple law enforcement sources familiar with preliminary investigation findings.

So far, there is no known connection to international or domestic terrorism, and it does not appear to be connected to the recent verdict in the , the sources said.

How the disaster unfolded

Families, including children in strollers, bundled up in the chilly wind and lined the parade route on Main Street.

The city's live stream of the parade showed a marching band had just started playing "Jingle Bells" . Onlookers shrieked in horror.

Another video captured by a paradegoer showed a young girl in a pink coat and hat dancing in the street as the SUV sped by, missing her by just a few feet.

Another witness, Nathan Bryce, captured .

On Monday morning, the belongings of paradegoers were still strewn across the scene as authorities try to confirm what led up to the calamity.

Police Chief Daniel P. Thompson said officers are working with the Waukesha County Medical Examiner's Office to identify victims.

Thompson said there is "a person of interest in custody," but would not say whether it was the driver of the SUV nor if any arrests have been made.

"This is still a very fluid investigation," the chief told reporters Sunday night. He said children are among the injured.

A Waukesha police officer to try to stop the driver, and no bystanders were struck by the officer's gunfire, the chief said. Thompson added he doesn't believe any shots were fired from the vehicle.

"The scene is now safe and secure," Thompson said.

Victims include Milwaukee Dancing Grannies members

Authorities have not released any details of the five people killed, but the said some members of the group were among the victims.

"Our group was doing what they loved, performing in front of crowds in a parade putting smiles on faces of all ages, filling them with joy and happiness," .

"Those who died were extremely passionate Grannies," the group said.

"Our hearts are heavy at this most difficult time, as more information and updates become available it will be posted. Please keep them their families, friends, the Milwaukee Dancing Grannies and everyone who lives have forever changed in your thoughts and prayer."

At least several of the injured were in critical condition

Aurora Medical Center-Summit, a hospital in Waukesha County, said it was treating 13 patients as of Sunday night: three listed in critical condition, four in serious condition and six in fair condition. "We are deeply saddened by today's senseless tragedy and our hearts are with the Waukesha community," the hospital said in a statement.

Froedtert Hospital in Milwaukee -- the only Level I trauma center in southeast Wisconsin -- said it was also treating patients from the parade incident but is not providing a specific number nor conditions. Level I trauma centers typically care for the most critically ill patients.

'It hit at least two people right away and rolled over them'

A shows the moment the vehicle struck pedestrians. A red SUV is seen hitting a person in a marching band. Then the vehicle continues forward, hitting and running over others in the band and crowd before driving away.

Angela O'Boyle, who lives in an apartment on the fifth floor which overlooks the parade route, told CNN she was on the balcony watching the festivities.

"The next thing I heard were screams, and turned my head and saw the car come and plow into the band that was just past my balcony at that point," she said."

"It hit at least two people right away and rolled over them. And then continued down the road to People's Park which is at the end of the block -- and then kept going, it didn't stop."

Boyle said she heard screaming and people yelling out their children's names, adding "it was not something that I wanted to see ... a little freaked out."

Kaylee Staral, a Milwaukee Journal Sentinel intern who , said "probably around 20 to 30 minutes into the parade, a red SUV came running down the middle of the street -- there were a lot of screams -- and we almost thought maybe it was Santa, but it was a red SUV and it hit a lot of people."

Staral went on to say "there were multiple people on the ground."

"Right in front of me in the little spot where I was sitting, probably four people were down, so there were a lot of people that ran to go check on them," Staral said. "I believe that the four people in front of me were still breathing but they were down, they were not moving."

Schools closed as a community mourns

Flags are to be flown at half-staff at "all buildings, grounds and military installations" statewide, Wisconsin Gov. Tony Evers said Monday.

"Today, I've ordered the 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," .

Roads in the area will remain closed for at least 24 hours, Thompson said. Businesses along the road where the calamity took place should remain closed Monday, city officials said.

The School District of Waukesha said it canceled classes on Monday and will determine if classes will resume Tuesday.

"The District will have additional counselors available during the school day at all buildings for all students that may be in need of support services," school officials said in a statement.

The White House is in touch with state and local officials, according to a White House official, and President Joe Biden has been briefed.

"The White House is closely monitoring the situation in Waukesha and our hearts go out to everyone who has been impacted by this terrible incident," a White House official said. "We have reached out to state and local officials to offer any support and assistance as needed."

The-CNN-Wire