Four people have been charged after two groups of demonstrators faced off against each other amid a heavy police presence at Nathan Phillips Square in Toronto.

Hundreds gathered at the downtown space Saturday afternoon after the event advertised on Facebook as "Let Trudeau know he has go to go!"

The page describes the goal of the rally as expressing opposition to everything from "soaring taxes to out of control spending" to the recent $10-million paid by the federal government to former Guantanamo Bay inmate Omar Khadr.

The event was not billed as anti-immigrant or anti-Islam and was marketed by organizer Ronny Cameron on his website as "exclusively about Justin Trudeau and all of the irresponsible decisions he has made as Prime Minister."

'Contempt for our history'

"Our economy is stagnant, our taxes are through the roof, our borders are being treated like door mats, free speech infringing motions like M-103 and bill C-16 have been passed, and worst of all we have a Prime Minister who displays nothing but contempt for our history and culture," the website reads.

But groups organizing against the event claimed the true intention behind it was "to normalize fear and hatred of Muslims and refugees."

The rally described its goal as voicing opposition to everything from "soaring taxes to out of control spending" to the recent $10-million dollars paid by the federal government to former Guantanamo Bay inmate Omar Khadr. (CBC)

"No more immigrants!" some demonstrators could be heard shouting amid the crowd.

"They may be out here to criticize Trudeau, but they're actually out here to say, 'We can't have refugees,'" said Sarah Ali, a member of Solidarity Against Facism Everywhere, which organized the counter demonstration along with Toronto General Defence Committee.

"You can have a criticism of foreign and domestic policy without being a fascist. But when you start to herald to a mythical white past, or when you start to associate with neo-Nazi or white supremacist groups, that's when you start crossing that line."

As the groups faced off, tensions mounted with at least one fight breaking out and an officer being assaulted, according to Toronto police.

'Pushing and pulling and tearing at each other'

Const. Allyson Douglas-Cook told CBC News one person was charged with assault of a peace officer, while another was charged with carrying a prohibited weapon such as pepper spray, and two others — who got into an altercation — with causing a disturbance. The officer who was allegedly assaulted was not seriously injured, she said.

One rally involved people opposed to the recent $10-million dollars paid by the federal government to former Guantanamo Bay inmate, Omar Khadr, while a counter protest involved an anti-racism group. (CBC)

"For a moment or two it was rather violent and the police interceded," Toronto police Staff Sgt. Chuck Konkel told CBC News.

"Passions took the better of people's actions and people got emotional, and people from both sides were pushing and pulling and tearing at each other."

It's unclear with which groups those arrested identified.

Konkel described the groups as "two sides of the coin."