A manhunt is underway in the US city of Chicago after a gunman killed and wounded people at an Independence Day parade in Highland Park.

At least six people were killed and 24 people wounded in a shooting at a July 4th parade in Higland Park, a suburb of the US city of Chicago, authorities said on Monday.

Police were searching for the gunman, and the city advised residents to shelter in place.

Lake County Major Crime Task Force spokesman Christopher Covelli said they believe there was only one shooter and warned that he should still be considered armed and dangerous.

Highland Park Mayor Nancy Rotering urged people to avoid the city centre.

"Numerous law enforcement officers are responding and have secured a perimeter around downtown Highland Park," the city administration said in a statement.

What we know

Shots were fired along the route only minutes after the parade to celebrate Independence Day began.

Covelli said the gunman apparently opened fire on parade-goers from a rooftop using a rifle that was recovered at the scene.

People, some visibly bloodied, fled the scene upon hearing several loud bangs, CBS 2 television of Chicago reported, citing a producer who was at the parade.

A Sun-Times reporter saw blankets placed over three bloodied bodies. Lake County Sheriff's office urged people to avoid the area to enable "law-enforcement and first responders to do their work."

"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," US Representative Brad Schneider, whose district includes Highland Park, said on Twitter. "Enough is enough!"

Gun violence in the United States

The shooting comes with gun violence fresh on the minds of many Americans.

Last month US President Joe Biden signed the first major federal gun reform law in three decades.

US Lawmakers reached the bipartisan agreement on gun control only weeks after a gunman in Buffalo, New York, opened fire on shoppers killing 10 people in what has been called a racist shooting.

Less than two weeks later, a shooter killed 19 children and two teachers at an elementary school in Uvalde, Texas.

Gun-related killings in the US are higher than in most other high-income countries. In 2019, for example, 4.12 people per 100,000 were killed by guns, while only 0.5 were killed in Canada.