MISSISSAUGA, Toronto (Reuters) - Canadian Prime Minister Justin Trudeau donned a bulletproof vest for an election campaign rally on Saturday, a Reuters eyewitness said, and the Canadian Broadcasting Corp. cited sources saying a security threat had been received.

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Pictures taken by Reuters photographer Stephane Mahe at the event in the Ontario city of Mississauga outside Toronto showed Trudeau wearing bulky protection under his shirt.

Police wearing backpacks surrounded Trudeau on stage for the first time since the start of a six-week election campaign leading up to what polls suggest will be a closely contested vote on Oct. 21.

The scenes were almost unprecedented in recent Canadian political history, which has been overwhelmingly peaceful.

CBC cited unnamed sources inside Trudeau’s Liberal Party as saying he donned the bulletproof vest after the campaign received a threat.

Liberal spokeswoman Zita Astravas declined to comment on Trudeau’s security arrangements. The Royal Canadian Mounted Police declined to comment.

Trudeau, who arrived 90 minutes late for the event, addressed the rally without incident. His wife Sophie had been due to introduce him but did not do so.

Trudeau, who often plunges into crowds to shake hands and pose for photos, did the same as he was leaving the event, but this time he was closely surrounded by security, said Mahe.

Unlike the United States, where four presidents have been assassinated since 1865, there is almost no history of serious political violence in Canada.

The one exception came in 1970, when a radical group seeking independence for Quebec kidnapped the Canadian province’s deputy premier and later killed him.

Trudeau will go ahead with plans to campaign in the Ontario city of York north of Toronto on Sunday, said a Liberal official who declined to be named given the sensitivity of the situation.

Polls show the Liberals are tied with the official opposition Conservatives of Andrew Scheer, who on Sunday said that if he won on Oct. 21 he would quickly move to end what he called government subsidies to rich corporations.