According to initial police reports, the gunman fired shots from a rooftop.
The building the gunman might have fired from was the building of a business, Crime Task Force spokesman Chris Covelli says. Access to the roof, he says, was not secure.
Covelli says it appears the gunman gained access to the rooftop by a ladder attached to the building.
Number of dead confirmed
Officials at the news conference also repeat the latest details of the number of people killed. It remains at six, officials confirm.
Five people died at the scene and one individual died at the hospital after suffering severe injuries, they add.
Specific area set out by police
Crime Task Force spokesman Christopher Covelli says a collaborative effort between local police, the FBI and other emergency services is under way and they have now demarcated a specific area within the state where people should remain in place.
Covelli says more people have now made it to hospital and the numbers of people injured might be slightly higher than originally reported when emergency services took them to be treated.
He says at this time there's no indication to make police think there was more than one gunman.
'Remain vigilant' - police warn community
We're hearing more from police and the coroner's team at the shooting in Highland Park, Illinois.
Commander Chris O'Neill from Highland Park Police says the area remains an active crime scene and repeats their call for people to stay at home.
He urges everyone to remain vigilant while the suspect is on the loose and also to report any suspicious behaviour in the community.
Anyone with knowledge of the scene of the shooting should contact the local authorities and the FBI, he says.
Parades cancelled all around...
By Marianna Brady, at the scene
Surrounding suburbs have cancelled their parades as a result of today's attack, she says.
The gunman is on the loose and with his next moves unknown.
The hospital is currently in lockdown because the authorities don't know the whereabouts of the gunman. He's been at large for five hours.
More than 20 people have been taken to the hospital and we're expecting an update on those numbers soon.
Biden vows to keep fighting gun violence
We're hearing some comments coming from US President Joe Biden now.
He says he has offered the full support of the federal government to help the community in Highland Park, after the shooting.
The president says he is 'shocked' over the parade shooting, and he vows to keep fighting gun violence in the US.
'Everybody's running all over frantically'
Wendi Kromash, a reporter with local paper Evanston Roundtable, spoke to one woman caught up in the chaos following the shooting on Monday.
Adrienne Drell had just picked a spot on Central Street in Highland Park to watch the parade.
Her spot was at the end of the route, not far from Sunset Park where post-parade activities were planned.
A marching band in blue and white uniforms passed by - and then, chaos unfolded.
“They [the band] had just come by and all of a sudden, the band disperses and kind of starts running and I'm thinking ‘That's how they're ending the parade?’
"Then they're running over my head and everyone says ‘Get out of here! Get out of here!’ And some older man came up and said ‘You gotta get out of here.’
"And then he picks me up, literally, shoving me away and then a cop came by with a dog and said, ‘Get out of here.’
Everybody's running all over frantically. And we heard that there were shooters.”
She adds there were people sheltering in place in the lobby of her apartment building.
"Everyone was shaken, saying ‘I can’t believe this, I can’t believe this happened.’
"It’s very jarring.”
What do we know about the rooftop position?
We know that the gunman is still at large, that people are being warned to stay indoors and that local and federal police are still hunting for him.
But what do we know about where he was at the time of the shooting?
Chris Covelli, spokesman for the Lake Country Major Crime Task Force says "it does appear he was shooting from a roof".
Commander Chris O'Neill of the local area's Highland Park Police says "firearms evidence was located on a rooftop of a nearby business".
'Enough is enough', - congressman at parade
Brad Schneider, a democrat who represent Illinois's 10th District in the US Congress, was at the start of the parade with his campaign team when the shooting began.
He tweets that: "Enough is enough".
"Today a shooter struck in Highland Park during the Independence Day parade," he writes.
"Hearing of loss of life and others injured.
"My condolences to the family and loved ones; my prayers for the injured and for my community."
The shooting in Highland Park follows on from two recent deadly attacks in Uvalde, Texas, and Buffalo, New York.
Firearms deaths are a fixture in American life.
In 2020 alone, more than 45,000 Americans died at the end of a barrel of a gun, whether by homicide or suicide, more than any other year on record. The figure represents a 25% increase from five years prior, and a 43% increase from 2010.
But the issue is a highly political one, pitting gun control advocates against sectors of the population fiercely protective of their constitutionally-enshrined right to bear arms.
Shooter 'discreet' with a 'high-powered rifle' - police
Crime Task Force spokesman Christopher Covelli also has some information on the people taken to hospital and the type of weapon used in the shooting - but he says he does not want to compromise any coming investigation.
He says some of the people being treated for injures are critical and some are serious.
He understands emergency responders ran towards the gunfire but the suspect stopped firing when they got close.
All indications are that he was "discreet and difficult to see", he says.
He says the weapon used was a high-powered rifle, but said he could not give further details.
The shooter targeted spectators and some of those marching in the parade, which was about three quarters of the way through when the shooting began, he says.
It was "very random, very intentional" and it's a "very sad day", he says.
'Tragic mass act of violence'
Today's shooting is a "tragic mass act of violence", Chris Covelli from the Lake County Major Crime Task Force says.
He says it is unclear what the suspect's intentions were and "we don't know if it could happen again".
Covelli emphasizes that according to the most up to date information, six people have been killed.
He says the focus of the investigation at this stage is on catching the suspect.
Covelli adds that there will be another news conference at 15:00 local time (20:00 GMT).
'We're hiding in a shelter now'
Anand P continues: "I rang my mom then and told her what happened and she came and quickly picked us up.
"We didn't hear anymore shooting after that time, so we got in the car and we came back to the parade area to see if people needed any help.
"Looking back, I was right next to the gun fire, we were literally not even 100m away from the shooter. It was so loud I could hear it so clearly.
"I feel stupid that we walked around and drove back to help people, because that person is still at large.
"I'm thinking about how I feel attending these large scale events now. I was at a pride parade a week ago and nothing bad happened, it was so safe, lots of police.
"I think people outside of Chicago don't understand Highland Park, it's very separate to the city. It's the suburbs, it's so safe, there is basically no gun crime, no violence. It's very liberal.
"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."
'We went to have a nice day out' - eyewitness
Eyewitness Anand P - who was paying an annual visit to his grandparents who live in the Highland Park area - tweeted that he was "feet away" from being shot.
were going to go to the parade - it's a really big deal, people come from all
over the place to watch the 4th of
July parade," he tells the BBC.
"I went with my two little cousins, they're
twins. We went to have a nice family day out - and then suddenly all this gunfire
about 5-10 seconds of very quick shots. I don't know much about guns, but it
sounded semi-automatic, 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.
"At the time
I personally wanted to believe it was a car backfiring. Then people
started running - so we start running.
"In the moment I wasn't scared, I had this
overwhelming feeling that I had to protect my cousins and that was my priority.
So we pick them up, we're running away and we hid behind a car in a parking
Reuters / TPX Images of the DayCopyright: Reuters / TPX Images of the Day
The US's federal police, the FBI, is working alongside local authorities in Highland Park to understand the situation, Chris Covelli, from the Lake County Major Crime Task Force, says.
He says close to 30 people have been transferred to hospitals. And he has information on the rifle used - saying it was high-powered.
The gunman is still at large and Covelli says the scene will remain "very active" while the attack itself was "very random, very intentional".
Majority of injured are treated for gunshot wounds - hospital
A hospital spokesperson tells the Reuters news agency there are 31 injured, mainly for gunshot wounds, but also some who were injured in the crush as people fled the scene of the Fourth of July parade.
Staff at North Shore Highland Park Hospital, in Highland Park, were treating 26 people while five were transported to North Shore Evanston Hospital, says spokesperson Jim Anthony.
"The vast majority suffered gunshot wounds. Remaining individuals sustained injuries as a result of chaos at the parade," Anthony says.
Gunman opened fire from a rooftop - initial reports
Initial reports suggest the gunman fired from a rooftop, police say.
Officers continue searching for a white male, believed to be aged between 18 and 20.
Where is Highland Park?
Highland Park is a suburban city in Illinois, about 25 miles (40km) north of central Chicago.
It's on Lake Michigan, and is home to a population of about 30,000.
It's been described as a quiet and affluent suburb of Chicago, and a stronghold of the Democratic Party.
In pictures: People abandon the scene
As we've been reporting, six people have been killed and a further 24 injured after a shooting in the Illinois city of Highland Park, north of Chicago.
People fled the Independence Day parade leaving their belongings behind.
Witness describes seeing injured people on ground
Witnesses have been speaking to reporters at the scene.
"We were walking up and we saw police. They shooed us away and they were running quietly around the corner," one young woman says.
"We walked a little closer. I saw someone on the ground with a girl crying next to him," she says.
"To my left, my Mum and I saw at least another three people on the ground," she says.