HIGHLAND PARK, Ill. — At least six people died and 24 were wounded in a shooting at a July Fourth parade in the Chicago suburb of Highland Park, and officers are searching for a suspect who likely fired on the festivities from a rooftop, police said Monday.

Highland Park Police Commander Chris O’Neill, the incident commander on scene, urged people to shelter in place as authorities search for the suspect.

Lake County Major Crime Task Force spokesman Christopher Covelli said at a news conference the gunman apparently opened fire on parade-goers from a rooftop using a “high-powered rifle” that was recovered at the scene. He didn’t know which building.

O’Neill said the shots were fired around 10:15 a.m., and Covelli said the parade was about three-quarters through when the shooter opened fire.

“Very random, very intentional and a very sad day,” he said.

Covelli said police believe there was only one shooter and warned that he should still be considered armed and dangerous, adding: “He could be in the city, he could be somewhere else.”

More than 100 law enforcement officers were called to the parade scene or dispatched to find the suspected shooter.

Hours after the shooting, with bystanders and media standing nearby, about a dozen officers suddenly dashed for a small office building half a block from where the shooting occurred — crouching at the glass doors, before flinging them open and rushing in, rifles pointed inside into a dark foyer. It was not immediately clear why the police had entered the building.

Police have not released any details about the victims or wounded.

“This morning at 10:14, our community was terrorized by an act of violence that has shaken us to our core,” Mayor Nancy Rotering said. “Our hearts go out to the families of the victims at this devastating time. On a day that we came together to celebrate community and freedom, we are instead mourning the tragic loss of life and struggling with the terror that was brought upon us.”

Illinois Gov. J.B. Pritzker said in a statement: “There are no words for the kind of monster who lies in wait and fires into a crowd of families with children celebrating a holiday with their community.”

The July 4 shooting was just the latest to shatter the rituals of American life. Schools, churches, grocery stores and now community parades have all become killing grounds in recent months. This time, the bloodshed came as the nation tried to find cause to celebrate its founding and the bonds that still hold it together.

President Joe Biden last month signed the widest-ranging gun violence bill passed by Congress in decades, a compromise that showed at once both progress on a long-intractable issue and the deep-seated partisan divide that persists.

In Highland Park, hundreds of parade-goers — some visibly bloodied — fled the parade route after shots rang out, leaving their belongings behind. Video shot by a Sun-Times journalist after the gunfire rang out shows a band on a float continuing to play as people run past, screaming.

As of early afternoon, ominous signs of a joyous event suddenly turned to horror filled both sides of Central Street where the shooting occurred. Dozens of baby strollers, some bearing American flags, abandoned children’s bikes, a helmet bedecked with images of Cinderella were left behind in their haste. Blankets, lawn chairs, coffees and water bottles were knocked over as people fled.

Police, some in camouflage gear and many clutching AR-style weapons, continued to pour into the area.

Armed FBI agents in camouflage escorted a family with two small girls across Central Street hours after the shooting. The children looked visibly frightened even as their mother attempted to reassure them that the agents leading and flanking them would protect them.

“Don’t worry, you’re safe now,” she told them. “These guys will protect you.”

Gina Troiani and her son were lined up with his daycare class ready to walk onto the parade route when she heard a loud sound that she believed was fireworks — until she heard people yell about a shooter.

“We just start running in the opposite direction,” she told The Associated Press.

Her 5-year-old son was riding his bike decorated with red and blue curled ribbons. He and other children in the group held small American flags. The city said on its website that the festivities were to include a children’s bike and pet parade.

Troiani said she pushed her son’s bike, running through the neighborhood to get back to their car.

In a video that Troiani shot on her phone, some of the kids are visibly startled at the loud noise and they scramble to the side of the road as a siren wails nearby.

It was just sort of chaos,” she said. “There were people that got separated from their families, looking for them. Others just dropped their wagons, grabbed their kids and started running.”

Debbie Glickman, a Highland Park resident, said she was on a parade float with coworkers and the group was preparing to turn onto the main route when she saw people running from the area.

“People started saying: ‘There’s a shooter, there’s a shooter, there’s a shooter,’” Glickman told the Associated Press. “So we just ran. We just ran. It’s like mass chaos down there.”

She didn’t hear any noises or see anyone who appeared to be injured.

“I’m so freaked out,” she said. “It’s just so sad.”