The mayor of Highland Park says the situation is “active” and urged people to remain indoors.
Several people have reportedly been shot at a 4 July Independence Day parade near the US city of Chicago.
The event in Highland Park, north of Chicago, was suddenly halted about 10 minutes after it began, when several shots were heard.
Congressman Brad Schneider, who represents the district, tweeted that he was “hearing of loss of life”.
One reporter saw five people with blood on them, according to the Chicago Sun-Times newspaper.
The mayor of Highland Park said the festival had been cancelled and asked people to avoid the downtown area.
Local resident Miles Zaremski told the Chicago Sun-Times: “I heard 20 to 25 shots, which were in rapid succession. So it couldn’t have been just a handgun or a shotgun.”
Pictures posted on social media suggest a large emergency services response has been sent to the area.