WILLOWBROOK, Illinois (AP) — At least 23 people were shot, one fatally, early Sunday during a gathering in a parking lot that drew hundreds of people in suburban Chicago, authorities said.

TV news video showed the strip mall lot in Willowbrook filled with debris and police tape, about 20 miles (32.1 kilometres) southwest of Chicago.

The DuPage County Sheriff’s Office described it as a “peaceful gathering” to celebrate Juneteenth that suddenly turned violent as a number of people fired multiple shots into the crowd.

“We know of 22 victims injured and one victim killed by gunfire. Several other victims were also injured while attempting to flee the area,” the sheriff’s office said in a statement.

Police were there monitoring the gathering but were called away because of a nearby fight, the sheriff’s office said.

“They heard gunshots and immediately returned to the scene,” the sheriff’s office said.

A motive for the attack wasn’t immediately known, and no one was arrested by early afternoon.

“We transported numerous victims from the scene. Others just walked into area hospitals,” said Eric Swanson, deputy chief at the sheriff’s office.

Rick Wagner, who lives nearby, said there were at least 300 people in the lot by 10:30 pm.

“We’ve had multiple conversations with police” about large groups meeting there, Wagner told the Daily Herald.

“It was like cars everywhere,” he said.

A witness, Markeshia Avery, said it was a Juneteenth celebration. Monday is the federal holiday commemorating the day in 1865 when enslaved people in Galveston, Texas, learned they had been freed — two years after the Emancipation Proclamation.

“We just started hearing shooting, so we dropped down until they stopped,” Avery told WLS-TV.

Another witness, Craig Lotcie, said: “Everybody ran, and it was chaos.”