Canadian prime minister Justin Trudeau has been criticised for changing his Twitter profile picture to a photo showing him sitting beside a black person.

The political leader’s re-election campaign has been rocked by the publication of old photos showing Mr Trudeau wearing blackface.

After apologising, Mr Trudeau was forced to admit he was unsure how many times he had darkened his face – and did not know if more photos might come to light.

Commenting on his recently-changed profile pic – which shows him smiling at a black man at a restaurant counter – some Twitter users accused Trudeau of trying to show he was friend and ally to minorities.

But a spokesperson for Mr Trudeau’s Liberal Party of Canada said the photo was changed on 11 September – prior to last week’s publication of the blackface images.

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Mr Trudeau attempted to forge ahead with his re-election campaign after polls showed a shift in voter support towards his Conservative rivals.

After several days of apologies, Mr Trudeau has resumed making campaign announcements, and was set to talk about health care in the Ontario city of Hamilton on Monday.

His Liberal Party of Canada campaign was completely knocked off course last week when Time magazine published a picture of him in brown makeup at a 2001 “Arabian Nights” party when he was a 29-year-old teacher. Two other images and a video of him in blackface later surfaced.

Justin Trudeau's new Twitter profile photo (@JustinTrudeau / Twitter)

The images prompted international ridicule and were at odds with his claims he wants to improve the lives of minorities in Canada.

“It’s a body blow,” pollster Frank Graves of EKOS Research said of the blackface images. “Will the Liberals be able to recover? Who knows? There’s no way of putting lipstick on a pig and making this go away.”

Mr Graves said his polling, which he has yet to publish in detail, shows a shift toward Conservative Party leader Andrew Scheer and away from Trudeau nationally.

Conservatives would win 35.5 per cent of the national vote and the Liberals 32.9 per cent, a Nanos Research poll released on Sunday said.

Trudeau, who launched his re-election campaign just over a week ago, said of the blackface incidents: ”I deeply regret that I did that. I should have known better but I didn’t.”