Ottawa: Canada's main opposition leader repeatedly attacked Prime Minister Justin Trudeau on Monday during a pivotal televised debate, calling him a phony and a fraud who did not deserve to be re-elected on October 21.

Opinion polls show Andrew Scheer's Conservatives have a real chance of defeating the ruling Liberals, whose campaign stumbled last month after images from years ago emerged showing Trudeau in blackface. Trudeau has repeatedly apologised for the images.

The two-hour debate - the only one to be held in English, the language spoken by two-thirds of Canada's 38 million population - has traditionally been regarded as an important way of winning the minds of voters.

In one of the few truly memorable moments, Scheer noted the Liberal leader had not at first disclosed how many times he had put on dark makeup.