Canadian Prime Minister Justin Trudeau apologized on Wednesday for wearing brownface makeup in 2001 after a picture emerged less than five weeks before a national vote in which he faces a tough fight for re-election.

"I should have known better then, but I didn't and I did it and I'm deeply sorry," Trudeau told reporters on his campaign plane in Halifax, Nova Scotia, after Time magazine published the image.

"Now I recognize it was something racist to do… This is something I deeply regret having done," said Trudeau.

Trudeau, a fervent advocate of the multiculturalism integral to Canadian identity, wore brownface makeup to a party at a school where he taught 18 years ago, Time magazine reported on Wednesday.

The report comes a week into a federal election campaign with Trudeau's Liberal Party in a tight contest against the Conservatives led by Andrew Scheer. Trudeau, 47, whose party won a landslide victory in 2015, has already been under attack for an ethics lapse and other controversies.

The photo showed Trudeau, then 29, wearing a turban and robes with his face, neck and hands darkened at an "Arabian Nights" gala in 2001.

The picture appears in the 2000-2001 yearbook of West Point Grey Academy, the magazine said. It cited Zita Astravas, of the Liberal Party's media relations division, as confirming Trudeau was in the photo "at the school's annual dinner which had a costume theme of 'Arabian Nights.'"

Trudeau is locked in a tight battle with Conservative leader Andrew Scheer ahead of the October 21 federal election. Scheer said he was "extremely shocked and disappointed" by the photo.

"Wearing brown face is an act of open mockery and racism. What Canadians saw this evening is someone with a complete lack of judgment and integrity and someone who's not fit to govern this country," he told reporters in Quebec.

Trudeau has seen his once sky-high popularity hurt by a series of missteps, including a ruling last month by a top watchdog that he had breached ethics rules by pressuring the former justice minister to ensure a major construction firm avoid a corruption trial.

Accusations of political meddling in a bribery case against engineering giant SNC-Lavalin plunged support for Trudeau at the beginning of the year.

The scandal broke when two members of his own cabinet accused him and his aides of meddling in the prosecution of SNC-Lavalin to save jobs.

Both the ministers were women and one was Canada's first indigenous attorney general. They were expelled from the party.

The episode cost Trudeau support among women, indigenous people and young people – constituents that helped propel him to victory in 2015.

Trudeau is the son of former prime minister Pierre Trudeau, who is considered the father of modern Canada. The younger Trudeau's stint as a teacher belonged to a colorful past that also included working as a snowboard instructor, a bartender and a bouncer.

(With input from Reuters and AFP)