At least 20 people were shot, one fatally, during a gathering in a car park in suburban Chicago, authorities said.
Local TV news showed the strip mall parking area filled with debris and police tape in Willowbrook, about 32km south-west of Chicago.
“There were at least 20 individuals shot. One victim is deceased,” said Eric Swanson, deputy chief at the DuPage County sheriff's office. “The motive behind this incident is unclear … We transported numerous victims from the scene. Others just walked into area hospitals.”
Witnesses say 20 to 30 gunshots were fired into a crowd of more than 200 teenagers and young adults early on Sunday.
“It was supposed to be like a Juneteenth celebration. We just started hearing shooting, so we dropped down until they stopped,” witness Markeshia Avery told WLS-TV. Juneteenth is a US public holiday on June 19 commemorating the emancipation of enslaved African Americans.
Another witness, Craig Lotcie, said: “Everybody ran, and it was chaos.”