At least six people were killed and dozens injured on Monday after a gunman fired on the crowd at a Fourth of July parade in Highland Park, Illinois.

It is believed that the gunman fired from a rooftop, law enforcement officials said, and they recovered a rifle from the scene. The suspect is still at large, and people in downtown Highland Park are being advised to shelter in place. The suspect, who has not yet been identified, is considered armed and dangerous, and SWAT teams are going from door to door in the area to try to find them, Lake County Sheriff’s Office Deputy Chief Christopher Covelli told reporters. “By all means, at this point, this appears to be completely random,” he added.

At least 31 people are being treated for injuries at two area hospitals, The Washington Post reports. In response to the shooting, several nearby communities canceled their own Fourth of July events. “On a day that we came together to celebrate community and freedom, we’re instead mourning the loss, the tragic loss of life, and struggling with the terror that was brought upon us,” Highland Park Mayor Nancy Rotering said.

Highland Park resident Miles Zaremski told The New York Times he heard the gunfire, and thought “it was a backfire or maybe was a firecracker, but then all of a sudden there was a stampede of the crowd who was attending on either side of the street. So I kind of gingerly walked up, and all of a sudden I saw people bloodied.” He added, “I have never seen anything like that in my life. It was chaos.”

Highland Park is about 25 miles north of downtown Chicago, with a population of 30,000.

This is a breaking news story. Please check back for new developments.