Four people were “very, very ill” and in hospital on Tuesday, a local official in Liverpool said, a day after a car drove into an enormous crowd of elated soccer fans in the city in northwest England.

Dozens more were injured in the incident on Monday evening, which the British police are not treating as terrorism. The police moved quickly to announce that they had arrested the driver of the car, a 53-year-old white man from Britain, in an apparent move to stop the spread of misinformation.

The collision ripped through what should have been a jubilant day for the city. Hundreds of thousands of people had gathered on Monday, a public holiday, to celebrate Liverpool F.C.’s victory in the Premier League, which is the top tier of British soccer.

Prime Minister Keir Starmer described the scenes as “appalling.”

Here is what we know.

What happened?

The Merseyside Police said they were contacted at about 6 p.m. on Monday local time after reports that a car had hit the crowd.

Video shared on social media shows a dark-color vehicle with a broken rear window swerving into the crowd and hitting parade-goers, leaving bodies on the ground. The video shows people rushing to aid the victims, including some who were trapped beneath the vehicle, and surrounding the vehicle once it stopped.

Video also shows witnesses attempting to stop the vehicle, with one person prying open the driver’s-side door before a man in the seat slams the door shut and accelerates into the crowd.

At a news conference on Monday, Assistant Chief Constable Jenny Sims of the Merseyside Police said: “What I can tell you is that we believe this to be an isolated incident and we are not currently looking for anyone else in connection with it. The incident is not being treated as terrorism.”

Who is the suspect?

The police said that the car stopped at the scene and that a “53-year-old white British man from the Liverpool area” had been arrested.

“We believe him to be the driver of the vehicle,” Ms. Sims confirmed at the news conference.

The police have not identified the man.

What do we know about the injured?

Forty-seven people were injured in the crash, including four children, the ambulance service said on Monday night.

Twenty-seven of them were taken to hospitals, two of whom — including one child — had sustained serious injuries, the authorities said on Monday.

Steve Rotheram, mayor of the Liverpool City Region, told the BBC on Tuesday morning that four people in the hospital were still “very, very ill.”

“We are hoping, of course, that they pull through,” he said.

Twenty others were treated at the scene with minor injuries. A paramedic on a cycle was also struck by the vehicle, but did not sustain any serious injuries.

Four people were temporarily trapped under the vehicle, including one child, the fire and rescue service said.

Officials have not yet identified any of the victims.

Where did it happen?

The ramming happened along Water Street in the Liverpool city center, near the end of the 10-mile parade route.

What have officials said?

“The scenes in Liverpool are appalling,” Prime Minister Keir Starmer of Britain wrote on social media on Monday night. “My thoughts are with all those injured or affected.”

Liam Robinson, a member of the Liverpool City Council, said in a statement that the episode had “cast a very dark shadow on what’s been a joyous day for the city.”

Liverpool F.C. wrote on X that it was in direct contact with the police. “We will continue to offer our full support to the emergency services and local authorities who are dealing with this incident,” it said.