Twelve people were arrested during a protest in Toronto on Friday over a debate that featured one of the masterminds of U.S. President Donald Trump's election.

Police said in a tweet the 12 people will face "various charges." The same tweet said two officers were injured during the protests — one was hit with a stick, the other was punched in the face. Their injuries are "fairly minor," police said. No other injuries were reported.

Roads around the downtown venue, Roy Thomson Hall, were closed but have since have reopened.

A protester is seen in handcuffs outside Roy Thomson Hall, ahead of the debate. (Evan Mitsui/CBC)

Hundreds of protesters descended on the downtown concert hall to voice their opposition to the debate between former Trump strategist Steve Bannon and former George W. Bush aide and speech writer David Frum.

As the attendees arrived, the crowd of protesters grew to the point where police lined two deep between them and those waiting in line to enter.

Protesters chanted, booed and jeered at those waiting in line, and held up signs with slogans such as, "refugees are welcome," and "human rights are not up for debate."

Police used pepper spray to subdue some protesters.

The dramatic scene outside the Munk Debate slowed entry to the venue, and the event started some 45 minutes late, at 7:30 p.m. ET.

Police stand between patrons in line and protesters on the street at Roy Thomson Hall in downtown Toronto. (Haweya Fadal/CBC)

Bannon debated Frum on whether populism is the future of Western politics. ​Bannon argued for the proposition; Frum against.

But the strife outside reached inside, as one protester on a balcony began shouting as Bannon started his opening statement. She was escorted from the venue.

Bannon acknowledged protesters' right to free speech, before emphatically stating that populism is "a new political revolution." The question to be asked, he said, is what kind of populism will take root?

"It's not a question of whether populism is on the rise and whether populism is going to be the political future," Bannon said. "The only question before us is, is it going to be populist nationalism or populist socialism?"

He attacked what he called the "permanent political class" that was running Washington, D.C., blaming it for the financial crisis and the years-long wars in Iraq and Afghanistan, and described the populist movement as the time for power to shift to "the little guy."

But he denied charges that populism is marked by racism and xenophobia.

"It's not," he said. "They're the backbone of our country, the most decent people on earth." Comments like these spurred ripples of laughter through the nearly 3,000-strong crowd.

In response, Frum said the rise of populist politics poses "the most important, the most dangerous challenge that liberal democratic institutions have faced since the fall of communism."

"To those who are undecided about populism's future and whether it has something useful to offer," Frum warned, "I'm here tonight to tell you it offers you nothing. It does not care about you, it does not respect you."

Speaking passionately with a waver in his voice at times, Frum said populism "claims to speak for the people, but it always begins by subdividing the people.

"Populism begins by dividing the country between 'those people' and 'us people.'"

Some protesters came in from Hamilton to voice opposition to the Munk Debate. (Rob Krbavac/CBC)

Bannon has long been a lightning rod for criticism of the alt-right movement, which he gave a home to in the form of his far-right news and opinion website, Breitbart. He was also Trump's chief strategist until he left the White House last year.

He has since established The Movement, a foundation devoted to promoting economic nationalism and far-right populism around the world.

But Frum's presence was also not without controversy over his role as a strategist and speechwriter for former U.S. president George W. Bush.

While the Munk Debates are a popular event for the city's political movers and shakers, the announcement of Bannon's participation back in September sparked an immediate backlash.

A petition opposing Bannon's participation garnered hundreds of signatures, while earlier this week, the federal NDP called for the debate's outright cancellation.

Hours before the debate, a consortium of groups led by No One Is Illegal, released a petition opposing the event that had some 5,000 signatures.

The group also organized the protest outside the venue that began at 5 p.m. The first protester arrived before 4:30 p.m., holding a sign reading "just say no to hate," with a photo of Bannon beside an equal sign next to a photo of a garbage can.

Rudyard Griffiths, the chair of the Munk Debates, had previously defended the event, saying it's "providing a public service by allowing their ideas to be vigorously contested and letting the public draw their own conclusions from the debate."

"Civil and substantive public debate of the big issues of our time helps all of us better understand the challenges we face as a society and what, if anything, can be done to resolve them," he said.

The first protesters gathered outside Roy Thomson Hall hours before the debate. (Evan Mitsui/CBC)

With files from Haweya Fadal and Mark Gollom