Six people have been shot dead at a 4 July Independence Day parade near the US city of Chicago, city officials say.
The event in the city of Highland Park was suddenly halted about 10 minutes after it began, when several shots were heard.
Police officials said they were still searching for a white man, aged 18-20, described as “armed and dangerous”.
City authorities said 24 people had also been hospitalised.
“This is an active incident,” officials said in an update posted to Highland Park’s website, advising those in the area to “shelter in place.”
Residents have been urged to stay at home and contact their loved ones to make sure they are safe.
Law enforcement officers, who are searching for the suspect, have secured a perimeter around Highland Park’s downtown area and recovered “evidence of a firearm,” the statement said.
At around 10:15 local (15:15 GMT) officials say the suspected shooter opened fire at the parade, which was scheduled to include floats, marching bands, and community entertainment as the city near Chicago celebrated Independence Day.
The suspect is believed to have fired at parade-goers from a nearby rooftop, police said.
Speaking at a press conference at 13:00 local time (18:00 GMT), local police spokesman Christopher Covelli said the suspected shooter was “armed and dangerous.”
He described him as a white male aged between 18 and 20 who appeared to have targeted the parade’s attendees at random.
“On a day that we came together to celebrate community and freedom, we’re instead mourning the tragic loss of life,” said city mayor Nancy Rotering.
Witnesses at the scene described the terrifying moment they heard multiple shots fired in quick succession.
Anand, who said he was less than 100m (328ft) from the shooter, told the BBC he initially thought he had heard a car backfiring before he saw others running and realised what was unfolding.
It was “the type of gun where it releases a lot of bullets in a very short amount of time. Incredibly loud. Then there’s complete silence,” he said.
Gun violence is very rare in this suburban area, he added: “I felt so safe here and this is very surreal. We’re hiding in a shelter now keeping safe, there’s people crying. It’s not a good feeling, at all.”
Speaking to local television station WGN, a witness called Michael said: “Immediately to the left of us he started shooting again and a woman went down.”
The mayor of Highland Park said the festival had been cancelled and asked people to avoid the downtown area.
Nearby suburbs have also gone on lockdown, with beaches evacuated, local parades and fireworks shows cancelled.
Gun violence in Chicago tends to rise over holiday weekends – as the hot weather sends people outdoors. In 2021, more than 100 people were shot and 17 killed over the Fourth of July weekend in the city of Chicago.
The shooting comes just a month after the deadly shootings in Uvalde, Texas and Buffalo, New York – and a week after the US Congress passed the first bipartisan legislation on guns in America.
