Witnesses have described the "horrendous" moment a car "rammed" into crowds of people who were attending Liverpool FC's victory parade following their Premier League win.
Merseyside Police said a number of pedestrians were hit by the vehicle in Water Street, Liverpool just after 18:00 BST.
A 53-year-old white British man from the Liverpool area was arrested, police said.
One eyewitness, BBC reporter Matt Cole, said the car missed him and his family "by literally inches".
"We had just moments before watched fireworks going off, the celebrations of the Liverpool bus passing us on the Strand," he said.
He said an ambulance had just made its way through the "dense" crowd he was part of on Water Street, when "there were screams ahead of us and suddenly this dark blue car just came through the crowd".
"It just wasn't stopping - I managed to grab my daughter who was with me and jump out of the way.
"It missed myself and my family by literally inches."
He said the ambulance acted like a "natural barrier... that slowed the car down", but that it had "no intention - it appeared - of stopping". He added that the car looked to be travelling at "more than 20 [mph]", but that he could not be sure it was not 30mph.
"As it passed me, it was being chased by a group of men who were trying to bang on the side of it and throw things at it," he explained, adding that the rear windshield had been "completely smashed in".
Having moved to safety down a side street, he saw police "running from all over, ambulances, police vans... more and more ambulances, more and more police vans - at one point then an entire squad of armed police cars stopped and people jumped out with rifles and again big medical packs on and began running towards the scene of the incident."
He said his initial assumption was that the driver just wanted to "barge through crowds because they didn't want to wait".
"But suddenly then, the speed registered and the shouts of the people and the screams of the people registered, and at that point, yeah, adrenaline very much just kicks in".
Harry Rashid, 48, from Solihull, was at the parade with his wife and two young daughters when he witnessed the car pull up before it "just rammed into all the people at the side of us".
He told PA news agency: "It was extremely fast. Initially, we just heard the pop, pop, pop of people just being knocked off the bonnet of a car.... I saw people on lying on the ground, people unconscious.
"It was horrendous. So horrendous."
Another witness, Mike Maddra, was walking with a group of friends, when he saw a car "speeding up" and hitting pedestrians.
He said the "car turned left, mounted pavement, come towards us and runs towards the buildings".
He added that he thought he saw two people being hit, and that "it looked deliberate".
"It has just ruined the day really," he said.