By Douglas Belkin , Joe Barrett and Alison Sider Updated July 4, 2022 3:20 pm ET

At least six people were killed and more than two dozen wounded in the Chicago suburb of Highland Park Monday morning after a gunman opened fire from a rooftop at a Fourth of July parade, according to local authorities.

Police are searching for the suspect, who is considered armed and dangerous, Chris Covelli, deputy chief of the sheriff’s department in surrounding Lake County, said at a press conference. He said a rifle had been recovered from the scene.

Chris O’Neill, the Highland Park Police incident commander, described the suspect as a white man between the ages of 18 and 20 with long black hair and a small build.

Officers are going door-to-door in the neighborhood to try to find the suspect, Mr. Covelli said.

NorthShore Highland Park Hospital is treating 26 people as a result of the mass shooting, spokesman Jim Anthony said. Five more people were transported to NorthShore Evanston Hospital, part of the same health system, Mr. Anthony said.

“A vast majority suffered gunshot wounds and the remaining sustained injuries as a result of the ensuing chaos at the parade,” Mr. Anthony said.

Witnesses said when they initially heard the sound of gunshots, they assumed that they were fireworks.

Among them was Illinois State Sen. Julie Morrison, whose district includes Highland Park. She was just setting out on the parade route in a convertible with her adult children, grandchildren and staff members when she heard the noise.

Then two women came running backward along the route, screaming, “‘There’s a shooter, there’s a shooter,’” Ms. Morrison said.

“I just couldn’t even register that that was a possibility,” she recalled. “We were kind of frozen in place and then there was this wave of people, this whole rush of moms and dads, they’re screaming and carrying their kids and running. And we knew it was a real thing.”

Ms. Morrison at first got down on the floor of the car and then, after everyone was accounted for, she and her group left the area.

“I will never subject my family or my friends or my volunteers to anything like that again,” the Democrat said. “Unfortunately, that’s just the way our world is now. And we need to step up and take action to change it.”

First responders at the scene of a shooting at a Fourth of July parade in Highland Park, Ill.Photo: Jim Vondruska/Getty Images By Douglas Belkin , Joe Barrett and Alison Sider Updated July 4, 2022 3:20 pm ET

At least six people were killed and more than two dozen wounded in the Chicago suburb of Highland Park Monday morning after a gunman opened fire from a rooftop at a Fourth of July parade, according to local authorities.

Police are searching for the suspect, who is considered armed and dangerous, Chris Covelli, deputy chief of the sheriff’s department in surrounding Lake County, said at a press conference. He said a rifle had been recovered from the scene.

Chris O’Neill, the Highland Park Police incident commander, described the suspect as a white man between the ages of 18 and 20 with long black hair and a small build.

Officers are going door-to-door in the neighborhood to try to find the suspect, Mr. Covelli said. Newsletter Sign-up The 10-Point.

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NorthShore Highland Park Hospital is treating 26 people as a result of the mass shooting, spokesman Jim Anthony said. Five more people were transported to NorthShore Evanston Hospital, part of the same health system, Mr. Anthony said. Police deployed after gunfire erupted at the parade in Highland Park, an affluent city of 30,000 near Chicago.Photo: WLS-TV/ABC7/via REUTERS

“A vast majority suffered gunshot wounds and the remaining sustained injuries as a result of the ensuing chaos at the parade,” Mr. Anthony said.

Witnesses said when they initially heard the sound of gunshots, they assumed that they were fireworks.

Among them was Illinois State Sen. Julie Morrison, whose district includes Highland Park. She was just setting out on the parade route in a convertible with her adult children, grandchildren and staff members when she heard the noise.

Then two women came running backward along the route, screaming, “‘There’s a shooter, there’s a shooter,’” Ms. Morrison said.

“I just couldn’t even register that that was a possibility,” she recalled. “We were kind of frozen in place and then there was this wave of people, this whole rush of moms and dads, they’re screaming and carrying their kids and running. And we knew it was a real thing.”

Ms. Morrison at first got down on the floor of the car and then, after everyone was accounted for, she and her group left the area.

“I will never subject my family or my friends or my volunteers to anything like that again,” the Democrat said. “Unfortunately, that’s just the way our world is now. And we need to step up and take action to change it.” People abandoned their belongings when they fled the shooting at the parade in Highland Park.Photo: Jim Vondruska/Getty Images

Videos shared on social media appeared to show bloodied parade-goers fleeing the parade in Highland Park’s downtown area, leaving behind chairs, blankets and strollers.

Hilary Stevens, who was at the parade with her husband and two children, recalled hearing 20 to 30 “pops” five to 10 minutes after the parade started. Suddenly, people started screaming and running. She and her family grabbed what they could and ran.

“People were trying to run into any buildings they could, and of course everything is locked,” she said. Ms. Stevens and her family hid behind some bushes, while her six-year-old cried.

Highland Park, an affluent city of 30,000 about 20 miles north of Chicago along Lake Michigan, canceled the Fourth of July event and asked people to avoid the area. Nearby towns including Evanston and Deerfield also canceled their Independence Day festivities.

“I ask all Illinoisans to pray for the families who have been devastated by the evil unleashed this morning in Highland Park,” said Illinois Gov. J.B. Pritzker. “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.”

Jan Wolfe contributed to this article.