A gunman armed with a high-powered rifle shot dead at least six people at a parade to mark US Independence Day in a wealthy Chicago suburb on Monday -- the latest in a series of shocking mass shootings on a holiday meant to celebrate all things American.

Police launched a manhunt in the city of Highland Park for the gunman, who was still on the loose, while authorities rushed to cancel July 4 celebrations there and in the nearby town of Evanston.

Along the parade route, abandoned chairs and other belongings could be seen scattered after panicked spectators fled for their lives.

"Everyone thought it was fireworks," one parade-goer, identified only as Zoe, told CNN.

"My dad thought it was part of the show, and I'm like, 'Dad, no... something is wrong.' And I grabbed him. And I looked back at him, and then it was just a sea of panic, and people just falling and falling."

As they ran, she said that some 20 feet behind her, "I saw a girl shot and killed... saw her die."

Zoe said they first hid behind a dumpster before police pulled them into the basement of a sporting goods store with some other people, several of whom were injured, including a man who appeared to have been shot in the ear and a girl who was shot in the leg.

When they were finally able to leave, she told CNN, the parade route resembled "a battle zone. And it's disgusting."

Police officials said the shooting began around 10:14 am, as the parade was approximately three-quarters of the way through.

"It sounds like spectators were targeted... So, very random, very intentional and very sad," said Lake County Major Crime Task Force spokesman Christopher Covelli.

Two dozen people were hospitalized, and six confirmed dead. Lake County coroner Jennifer Banek said five of them, all adults, had died at the scene. The sixth was taken to hospital but died later.

Police said the shooter was using a "high-powered rifle," and "firearm evidence" had been located on a nearby rooftop.

"All indications is he was discreet, he was very difficult to see," said Covelli.

First responders at the scene of a shooting at a parade on July 4, 2022 in Highland Park, Illinois
First responders at the scene of a shooting at a parade on July 4, 2022 in Highland Park, Illinois GETTY IMAGES NORTH AMERICA via AFP / Jim Vondruska

Nancy Rotering -- the mayor of Highland Park, a wealthy suburb north of Chicago in the Midwestern state of Illinois -- gave the same toll and condemned the holiday violence.

"On a day that we came together to celebrate community and freedom, we're instead mourning the tragic loss of life and struggling with the terror that was brought upon us," she said.

Multiple law enforcement agencies, including the FBI, the state police and the local sheriff's office, are assisting with the response.

Highland Park announced that all July 4 festivities had been canceled as a result of the violence, as did nearby Evanston.

"While there is no known threat to Evanston residents, the shooter is still at large; therefore, cancelations are taking place in an abundance of caution," the city said.

US Representative Brad Schneider, who was at the parade, said on Twitter that "a shooter struck in Highland Park during the Independence Day parade."

"Hearing of loss of life and others injured. My condolences to the family and loved ones; my prayers for the injured and for my community," he wrote, adding: "Enough is enough!"

The shooting is part of a wave of gun violence plaguing the United States, where approximately 40,000 deaths a year are caused by firearms, including suicides, according to the Gun Violence Archive website.

The debate over gun control -- a deeply divisive issue in the country -- was reignited by two massacres in May that saw 10 Black supermarket shoppers gunned down in upstate New York and 21 people, mostly young children, slain at an elementary school in Texas.

Congress passed the first significant bill on gun safety in decades in the wake of those killings. President Joe Biden signed it into law in late June, saying that while it falls short of what is really needed, it will still save lives.

But a day earlier, proponents of tougher firearms laws suffered a setback when the US Supreme Court ruled that Americans have a fundamental right to carry a handgun in public, a landmark decision with far-reaching implications for states and cities across the country trying to rein in gun violence.