The image of a 29-year-old Trudeau with his face in dark make-up is a major challenge for a leader who often speaks about the need to fight racial discrimination and who has three prominent ministers of Indian descent in his cabinet.

"I should have known better then, but I didn't and I did it and I'm deeply sorry," Trudeau, 47, told reporters on his campaign plane in Halifax, Nova Scotia, after Time magazine published the image.

Time said the image was provided by Vancouver businessman Michael Adamson earlier this month. Adamson was part of the West Point Grey Academy community where Trudeau, then 29, worked at the time, the magazine said. The picture was in the Vancouver private school's yearbook.

"I dressed up in an Aladdin costume and put make-up on. I shouldn't have done it," Trudeau said in comments carried live on Canadian television.

The picture shows him wearing a turban and a white robe, with his face covered in dark make-up.

Trudeau, questioned by reporters, also admitted he had dressed up in make-up when at high school and performed "Day O", a traditional Jamaican song about people loading bananas onto boats.

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.

Australian Associated Press