Police arrested a suspect Monday after a mass shooting left six dead at a US Independence Day parade in a wealthy Chicago suburb, casting a dark shadow over the country's most patriotic holiday.

Robert Crimo, 22, was identified as a "person of interest" and became the target of a massive manhunt across the town of Highland Park in Illinois, where a rooftop gunman with a high-powered rifle turned a family-focused July 4 parade celebration into a scene of death and trauma.

Firing into the holiday crowd, the shooter triggered scenes of total chaos as panicked onlookers ran for their lives, leaving behind a parade route strewn with chairs, abandoned balloons and personal belongings.

Emergency officials said around two dozen people, including children, were treated for gunshot injuries, with some in critical condition.

After a brief car chase, Crimo was taken into custody "without incident," Highland Park police chief Lou Jogmen told reporters.

Earlier, police had warned that he was armed and "very dangerous." A Chicago musician of the same age and with the same name goes by the stage moniker "Awake the Rapper" online.

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, according to the Gun Violence Archive website.

And it cast a pall over America's Independence Day, in which towns and cities across the country hold similar parades and people -- many dressed in variations on the US flag -- hold barbecues, attend sports events and gather for firework displays.

"We were getting ready to march down the street and then all the sudden waves of these people started running after, like running towards us. And right before that happened, we heard the pop, pop, pop, pop, pop, and I thought it was fireworks," Emily Prazak, who marched in the parade, told AFP.

A police officer searches the scene of the Fourth of July parade shooting in Highland Park, Illinois on July 4, 2022
A police officer searches the scene of the Fourth of July parade shooting in Highland Park, Illinois on July 4, 2022

Don Johnson, who attended the parade, said he initially thought the gunshots were a car backfiring.

"And finally, I heard the screams from a block down and people running and carrying their kids and everything, and we ran into the gas station, and we were in there for three hours," he told AFP.

"I've seen scenes like this over and over again on the TV and in different communities, and didn't think it was going to happen here ever," he said.

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

Abandoned lawn chairs stand along the streets at the scene of the Fourth of July parade shooting in Highland Park, Illinois on July 4, 2022
Abandoned lawn chairs stand along the streets at the scene of the Fourth of July parade shooting in Highland Park, Illinois on July 4, 2022

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

Five of the six people killed, all adults, had died at the scene. The sixth was taken to hospital but succumbed to wounds there.

Dr Brigham Temple of Highland Park Hospital, where most of the victims were taken, said that it had received 25 people with gunshot wounds aged eight to 85.

He said "four or five" children were among them, and that 16 people were later discharged.

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

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

A Mexican was among those killed, Mexico's Foreign Minister Marcelo Ebrard said.

"We stand with the Chicago community in its pain and sadness over this tragedy," he tweeted.

An Independence Day ballon with the words "God Bless America" is seen along the parade route at the scene of the Fourth of July parade shooting in Highland Park, Illinois on July 4, 2022
An Independence Day ballon with the words "God Bless America" is seen along the parade route at the scene of the Fourth of July parade shooting in Highland Park, Illinois on July 4, 2022

President Joe Biden voiced his shock and vowed to keep fighting "the epidemic of gun violence" sweeping the country.

"I'm not going to give up," he said.

Last week, Biden signed the first significant federal bill on gun safety in decades, just days after the Supreme Court ruled that Americans have a fundamental right to carry a handgun in public.

The deeply divisive debate over gun control 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.

According to the Gun Violence Archive, there have been 309 mass shootings carried out in the US so far in 2022 -- including at least three others on July 4, though without any fatalities.

"It is devastating that a celebration of America was ripped apart by our uniquely American plague," Illinois governor JB Pritzker told reporters Monday.

"A day dedicated to freedom has put into stark relief the one freedom we as a nation refuse to uphold -- the freedom of our fellow citizens to live without the daily fear of gun violence."

Location of Highland Park, Illinois, where a shooter opened fire during a parade to mark US Independence Day
Location of Highland Park, Illinois, where a shooter opened fire during a parade to mark US Independence Day
Officers gather at the scene of the Fourth of July parade shooting in Highland Park, Illinois on July 4, 2022
Officers gather at the scene of the Fourth of July parade shooting in Highland Park, Illinois on July 4, 2022

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