A photo has emerged of Canadian prime minister Justin Trudeau wearing ‘brownface’ make-up to a party at a school where he was teaching in 2001, at a time when the leader is battling for re-election.

The yearbook picture, obtained by Time Magazine, shows a 29-year-old Mr Trudeau wearing a turban and skin-darkening make-up on his face, neck and hands for an Arabian Nights-themed costume party at the West Point Grey Academy in Vancouver.

The prime minister, who launched his re-election campaign just a week ago, said he should have known better.

“I’m pissed off at myself, I’m disappointed in myself,” Mr Trudeau told reporters travelling with him on his campaign plane.

A spokesperson for Mr Trudeau’s Liberal Party confirmed the validity of the photo to the magazine on Wednesday.

“It was a photo taken while he was teaching in Vancouver, at the school’s annual dinner which had a costume theme of Arabian Nights”, said media relations lead Zita Astravas.

“He attended with friends and colleagues dressed as a character from Aladdin,” she added.

The picture’s release comes as a critical time for Mr Trudeau as he campaigns for re-election on 21 October, with polls saying he faces a serious challenge from Conservative leader Andrew Scheer.

The 47-year-old son of late prime minister Pierre Trudeau is already vulnerable following one of the biggest scandals in Canadian political history, which arose when Mr Trudeau’s former attorney general said he improperly pressured her to halt the criminal prosecution of a company in Quebec.

The prime minister has said he was standing up for jobs.

Mr Trudeau has been admired by liberals around the world for his progressive policies in the Trump era, with Canada accepting more refugees than the United States. His Liberal government has also strongly advocated free trade.