(CNN) Ten people are dead and 15 are injured after the driver of a van plowed into multiple pedestrians in Toronto on Monday in what appears to be a deliberate act, Toronto Police Chief Mark Saunders said.

Saunders said the suspected driver, Alek Minassian, 25, of Richmond Hill, Ontario, was in custody. Minassian was arrested in a white rental van less than 30 minutes after police received a 911 call, Saunders said.

Minassian was previously known to Toronto authorities, according to a US law enforcement official briefed on the matter. Authorities said Minassian left a trail of destruction nearly a mile long, north of midtown Toronto.

Deputy Police Chief Peter Yuen said police received calls around 1:30 p.m. that a vehicle was driving on Yonge Street, striking pedestrians. Police said the collisions happened in the North York area at the busy intersection of Yonge Street and Finch Avenue.

"Based on witness accounts, we have a vehicle that started north on Yonge Street from Finch and drove southbound at some point in times on sidewalks, at some point in times driving southbound in northbound lanes," Saunders said.

Saunders added: "So, it's very clear just from a general perspective to say that the actions definitely look deliberate."

At this point, "There would appear to be no national security connection" to the incident, said Ralph Goodale, Canada's minister of public safety and emergency preparedness.

Ten patients were transported to Sunnybrook Health Sciences Centre and two were declared dead at the hospital, said Dr. Dan Cass, executive vice-president and chief medical officer.

Cass said the patients suffered a range of injuries.

Mayor: Incident is 'not representative of how we live'

"This is a time when the community should come together," said Toronto Mayor John Tory, who praised first responders.

Tory said he hopes Toronto remembers it is a city of inclusion.

"This kind of tragic incident is not representative of how we live or who we are ... or anything to do with life in this city on a day-to-day basis," Tory said.

Canadian Prime Minister Justin Trudeau offered his condolences to the families of the victims. Calling it a "tragic and senseless attack," he thanked first responders. They "faced danger without hesitation, and their efforts no doubt saved lives and prevented further injuries," he said.

"We should all feel safe walking in our cities and communities," Trudeau said. "We are monitoring this situation closely, and will continue working with our law enforcement partners around the country to ensure the safety and security of all Canadians."

The White House echoed the sentiments, saying in a statement that the United States "stands with the Canadian people in the aftermath of today's tragic event."

"Our thoughts and prayers go out to the families of those affected, and we wish a full recovery to those injured," the statement said. "The United States Government pledges to provide any support Canada may need."

In recent years, individuals have driven vehicles into crowds of pedestrians in fatal attacks in major cities including Barcelona, New York, London and Nice, France.

Chelsea Luelo, who works at Capriccio Café, saw the incident unfold in Toronto, and said she thought the driver was hitting people intentionally.

"It looked like he was going straight, halfway through the sidewalk," Luelo said.

Jonathan Mayor, a spokesman for Ryder, said the incident involved one of the company's rental vans.

"We take the safety and security related to the use of our entire fleet very seriously and we are cooperating fully with authorities," Mayor said in an email to CNN.

To our city, our people and all those affected by today's tragic events, our thoughts and prayers are with you. — Toronto Maple Leafs (@MapleLeafs) April 23, 2018

'Pandemonium broke loose'

Witness Mary Tan shared two photos showing people injured in the incident.

Another witness, Raj Irshad, said he saw multiple bodies on the ground.

Irshad works at an Esso gas station about a block from where the van is reported to have driven onto the sidewalk. He said he did not see the initial collision but saw the aftermath. He also saw multiple emergency vehicles in front of his gas station.

One witness told CNN network partner CTV that he was out for a cigarette when he saw the van hit a man walking through the intersection.

"And then, just pandemonium broke loose, just everyone was going crazy," he said. The vehicle was going 60 to 70 kph, he estimated.

One witness, who was driving at the time, said he at first thought the driver was having a heart attack until he saw the white van speeding and striking people on the sidewalk.

"He's just hitting people one by one, going down," the witness said. "It's a nightmare."

Bersat Noorai, the manager of Taftan Kebab, said he saw the white van hit the bench in front of his restaurant. He ran outside and saw two or three people on the ground.

One man, who appeared to be in his early 20s, was losing a lot of blood, and Noorai said he brought him a towel and water and called 911.

'She's face down on the concrete'

Another witness, Christian Ali, said he came onto the scene and saw bodies and evidence of the destruction.

He first saw a man unconscious at the side of the road and figured it was a terrible accident after also noticing debris from a car.

"Two blocks over, I saw another gentleman unconscious in the middle of the road and a policeman leaning over him holding his neck," Ali said.

About a block up, he saw a woman who looked like she had died.

"She's face down on the concrete, a lot of fluid coming out of her head," Ali said.

"About 20 seconds after that, I came upon a crowd of about 30 people ... probably about five people on the ground, bleeding," he said, adding that pedestrians were performing CPR.

'He died in our arms'

Diego DeMatos was one of the good Samaritans who tried to save victims.

DeMatos said he was on his way to the gym, driving north on Yonge when he saw the van driving fast southbound. He said he saw the van hit a man and a woman.

"Blood started gushing out of his head, and she was bleeding really badly, too," DeMatos said.

At first, he thought the collision was a hit-and-run, but he noticed four to five victims on the ground as he drove a few meters further.

"Some of them were moving, some of them were motionless," he said.

DeMatos said he stopped to help another victim, who was already being aided by someone.

"I went over to try to perform CPR on him. ... He died in our arms," DeMatos said.

"It was like a scene from a war zone. There was garbage cans everywhere, broken bus shelters and mailboxes on the ground."

One woman who was wearing a scarf took it off and gave it to them, DeMatos said, and they covered the victim.

Prayers for Toronto. ❤️ — Marcus Stroman (@MStrooo6) April 23, 2018

We are Toronto. pic.twitter.com/7SQphtidDb — Toronto Maple Leafs (@MapleLeafs) April 23, 2018

'Prayers for Toronto'

Canadian sports teams showed their support for victims in several ways.

The Toronto Maple Leafs held a moment of silence before their Stanley Cup Playoff game against the Boston Bruins. After the moment of silence, Martina Ortiz-Luis, who sang the Canadian national anthem, allowed the crowd to sing along.

"Although we are far from home, our hearts and minds are back in Toronto with those affected by today's tragic events," the Toronto FC soccer team wrote on Twitter.

"World is becoming scarier by the second. Should never have to question whether going outside for a walk is a bad idea or not. Prayers to Toronto for real!" Marcus Stroman, a pitcher for the Toronto Blue Jays, tweeted.