Justin Trudeau speaks at a campaign in Welland, Ontario, on Monday.
CNN  — 

After denouncing protesters as “anti-vaxxer mobs,” Canada’s Prime Minister Justin Trudeau was pelted with gravel at an election campaign stop on Monday night.

Journalists traveling with the Liberal Party leader posted videos of the incident in London, Ontario, as Trudeau was boarding his campaign bus after the event. Several videos show Trudeau surrounded by campaign aides and security as protesters continue shouting at him.

The video shows what Trudeau later described as “little bits of gravel” hitting him and others as he boards the bus.

The incident underscores a national election campaign that has been growing increasingly heated. Last month, Trudeau’s campaign canceled a public event for security reasons. Many protesters trailing Trudeau say they are angry with public health measures such as vaccine mandates.

Earlier Monday, Trudeau had said he would not “back down” from campaigning, despite dozens of loud and increasingly aggressive protesters stalking his events.

“Yes, there is a small fringe element in this country that is angry, that doesn’t believe in science, that is lashing out with racist, misogynistic attacks,” said Trudeau while campaigning in Ontario hours before the gravel-throwing incident.

High vaccination rate

Canada’s Conservative Party leader, Erin O’Toole, has denounced aggressive protesters saying last week that his party does not condone such behavior.

“I strongly condemn any form of harassment and protest the like we’ve seen. We’re a democracy, we should be having a healthy and respectful debate of ideas and we have no time for people who bring in negativity to campaigning,” he said during a news briefing.

After the incident, Canada’s ambassador to the United Nations, Bob Rae, tweeted that, “Our learned experience should teach us two things: political violence is contagious unless stopped in its tracks with both denunciation and enforcement, and it is wrong to think “this isn’t Canada”. Unfortunately it is and it will have terrible consequences unless we face up to it”.

Canada’s snap federal election is slated for September 20 – and polls show a close race between Trudeau and O’Toole’s political parties.

Most Canadians have embraced public health measures and Canada now has one of the highest vaccination rates in the world with 3 out of every 4 eligible Canadians fully vaccinated.

Despite that, the simmering pandemic is plaguing Canada with case counts and hospitalizations rising according to the Public Health Agency of Canada, especially among younger, unvaccinated Canadians.