Rooftop shooter kills 6 at July 4 parade in Chicago suburb of Highland Park

Six people were killed and at least two dozen injured when a rooftop gunman opened fire at a Fourth of July parade in the wealthy Chicago suburb of Highland Park on Monday, turning a civic display of patriotism into a scene of panicked mayhem.

Officials told a news conference that six people were killed and 24 taken to hospital and that a rifle was recovered from the scene. A hospital spokesperson reported 31 people were injured.

Police were searching for a white male, believed to be about 18 to 20 years old, and asked the public for tips to help find him.

"There are no words for the kind of monster who lies in wait and fires into a crowd of families with children celebrating a holiday with their community," Illinois Governor J.B. Pritzker said in a statement.

The shooting comes with gun violence fresh on the minds of many Americans, after a massacre on May 24 killed 19 school children and two teachers at an elementary school in Uvalde, Texas, and the May 14 attack that killed 10 people at a grocery store in Buffalo, New York.

Staff at NorthShore Highland Park Hospital in Highland Park were treating 26 people and five were transported to NorthShore Evanston Hospital, spokesperson Jim Anthony said.

"The vast majority suffered gunshot wounds. Remaining individuals sustained injuries as a result of chaos at the parade," Anthony said.

Children waving American flags, riding tricycles or enjoying a ride in a wagon pulled by adults froze as people in the crowd screamed while gun shots rang out, according to a video posted on social media.

Witness Amarani Garcia, who was at the parade with her young daughter, told the local ABC affiliate she heard gunfire nearby, then a pause for what she suspected was reloading, and then more shots again.

There were "people screaming and running. It was just really traumatizing," Garcia said. "I was very terrified. I hid with my daughter actually in a little store. It just makes me feel like we're not safe anymore."

Social media video showed a marching band in the parade suddenly breaking formation and running away, and other images of people leaving their belongings behind as they sought safety.

"Everyone was running, hiding and screaming," said CBS 2 Digital Producer Elyssa Kaufman, who was at the scene, the channel's website reported.

"It sounded like a string of about 20 firecrackers that were let off inside of your mental garbage bin, it was that loud," Jeff Leon, 57, told CNN, estimating the gunfire lasted less than a minute. "So, I didn't immediately react, I thought it was just how people are on the fourth."

Highland Park's population is 30,000 and nearly 90% white, according to the U.S. Census Bureau. About a third of the population is Jewish, according to the Jewish Telegraphic Agency.

The shooting is likely to rekindle the American debate about gun control, and whether stricter measure can prevent mass shootings that happen so frequently in the United States.

"Grief will not bring the victims back, and prayers alone will not put a stop to the terror of rampant gun violence in our country," Pritzker said. "I will stand firm with Illinoisans and Americans: we must - and we will - end this plague of gun violence."