Thousands of fans were lining the streets to celebrate the club winning the Premier League title at the time.
Here’s what we know so far.
Follow live: Man arrested after pedestrians hit during Liverpool parade
What happened?
Witnesses described a people carrier ploughing into crowds of people, who had been out celebrating in their tens of thousands on Monday.
Eyewitness Natasha Rinaldi heard “screams” and described bystanders rushing after the car to try to stop it.
Harry Rashid, who was at the parade with his family, said it was travelling “extremely fast”.
He added: “It was horrible. And you could hear the bumps as he was going over the people. Then my daughter started screaming and there were people on the ground. It looked clearly deliberate.”
Another witness, who was walking with a group of friends, said he saw a car “speeding up” and hitting pedestrians.
The man, who gave his name as Mike Maddra, told PA news agency the “car turned left, mounted pavement, come towards us and runs towards the buildings”.
When and where did it happen?
Merseyside Police were called just after 6pm on Bank Holiday Monday.
The incident happened on Water Street in the city centre – near Liverpool Town Hall and the Liver Building.
The procession – accompanied by heavy policing and security – had already spent hours making its way along a 10-mile (16km) route in the rain, snaking through a sea of red smoke and grey skies.
Police have put a vast cordon in place on Water Street.
What do we know about the driver?
Shortly before 8pm, Merseyside Police confirmed that a 53-year-old white British man from the Liverpool area had been arrested.
The force is urging the public “not to speculate on the circumstances surrounding tonight’s incident”.
What has the response been so far?
Prime Minister Keir Starmer said he was being updated on the situation and thanked police for their swift action.
“The scenes in Liverpool are appalling – my thoughts are with all those injured or affected,” he said.
Liverpool Football Club said it was in contact with the force and would “continue to offer our full support to the emergency services and local authorities who are dealing with this incident.”
Liverpool’s city rivals Everton FC said in a statement on social media: “Our thoughts are with all those who have been affected by this serious incident in our city.”
Home Secretary Yvette Cooper thanked police and called the incident “truly shocking and horrendous”.
“Thinking of all those affected at this very difficult time. The police are investigating and I’m being kept updated on developments.”
