At least six people have died and 30 have been injured after a gunman opened fire on a July 4 parade in suburban Chicago.

Hundreds of marchers, parents with strollers and children on bicycles fled the scene in Highland Park, a suburb in the city, on Monday. 

A 22-year-old has been identified as a person of interest and has been taken into custody, the city's police force confirmed. 

Highland Park Police chief Lou Jogmen earlier said Robert E Crimo III should be considered armed and dangerous and was pulled over by police on after a brief pursuit in the evening.

“It is devastating that a celebration of America was ripped apart by our uniquely American plague,” Illinois Governor JB Pritzker said at a news conference.

“I’m furious because it does not have to be this way… while we celebrate the Fourth of July just once a year, mass shootings have become a weekly — yes, weekly — American tradition.”

The shooting occurred at a spot on the parade route where many residents had staked out prime viewing points early in the day for the annual celebration.

Lake County Major Crime Task Force spokesman Christopher Covelli said at a news conference “several of the deceased victims” died at the scene and one was taken to a hospital and died there. Police have not released details about the victims or wounded.

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The Herald:

Lake County coroner Jennifer Banek said the five people killed at the parade were adults, but did not have information on the sixth victim who was taken to a hospital and died there.

One of those killed was a Mexican national, Roberto Velasco, Mexico’s director for North American affairs, said on Twitter on Monday. He said two other Mexicans were wounded.

NorthShore University Health Centre received 26 patients after the attack. All but one had gunshot wounds, said Dr Brigham Temple, medical director of emergency preparedness. Their ages ranged from 8 to 85, and Dr Temple estimated that four or five patients were children.

Dr Temple said 19 of them were treated and discharged. Others were transferred to other hospitals, while two patients, in stable condition, remained at the Highland Park hospital.

The gunman opened fire around 10.15 am, when the parade was about three-quarters through, authorities said.

Highland Park Police commander Chris O’Neill, the incident commander on scene, said the gunman apparently used a “high-powered rifle” to fire from a spot atop a commercial building where he was “very difficult to see”.

He said the rifle was recovered at the scene. Police also found a ladder attached to the building.

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

President Joe Biden on Monday said he and first lady Jill Biden were “shocked by the senseless gun violence that has yet again brought grief to an American community on this Independence Day”.