New Delhi: At least six people were killed and 24 injured after gunfire erupted at a July Fourth parade in an affluent Chicago suburb on Monday evening.

Police launched a massive manhunt to nab the culprit, authorities said.

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A high-powered rifle has been found, and police are searching for a gunman, described as a white man between the ages of 18 and 20 with long black hair, who opened fire at about 10:14 a.m. CDT, Highland Park police Commander Chris O’Neill told reporters.

Police had no idea that the shooter is holed up nearby and should be considered armed and dangerous, officials said.

The city of Highland Park confirmed that there’s “an active shooter incident” and urged all “individuals are advised to shelter in place.”

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Police were spotted scouring rooftops around Central Avenue near Green Bay Road and Second Street in the aftermath of the gunfire.

“It does appear that he was shooting from a roof,” Lake County Sheriff’s Deputy Chief Christopher Covelli told reporters. The shooter got to his elevated locale by scaling a ladder, attached to a building, Covelli added.

The parade included scores of police and fire personnel. Shortly after gunfire erupted, officers moved toward the elevated sniper — causing him to stop and flee.

“He was discreet and very difficult to see,” Covelli said.

Five of those six killed were pronounced dead at the scene while the sixth victim died a hospital, Lake County Coroner Jennifer Banek said.

Of the injured people, ten were taken to Highland Park Hospital, six to Lake Forest Hospital and seven to Evanston Hospital, Highland Park Fire Chief Joe Schrage said.

Paradegoers who might have lost contact with friends and family at the event were urged to go to the Highland Park Police Department to be reunited with them.

In the aftermath of Monday’s shooting, discarded camping chairs, American flags, plastic cups and other belongings littered the parade route, left behind by people who had come out to celebrate July Fourth before fleeing for their lives.

In the business district near the scene of the shooting, dozens of people were sheltering in place in businesses, awaiting SWAT teams who escorted them out to safety.

Helicopters circled overhead as the manhunt continued for the shooter who reigned terror on what was supposed to be a celebration of the nation’s freedom.