With less than five weeks to go before a national vote, Time magazine published a picture of Trudeau in brown face from a 2001 "Arabian Nights" party when he was a 29-year-old teacher at a Vancouver private school.

After apologising to Canadians in a hastily staged meeting with the media on his campaign plane on Wednesday, Trudeau held a conference call for all his 338 candidates on Thursday.

"The prime minister expressed his apology and regret and said this happened 20 years ago," one Liberal who was on the call said.

"He said this is the moment for us to continue to work together to understand the pain of people who are on the receiving end of racism and stereotypes."

The Liberal leader has two campaign events planned for later on Thursday, and is due to speak to reporters at an event in Winnipeg, Manitoba, at 2.15pm local time.

Even before the brown-face scandal, the race going into the October 21 vote was tight.

But the release of the bombshell images could be a turning point, in part because Liberals have traditionally attracted support from immigrant communities.

Head of EKOS Research polling company Frank Graves said the images were clearly damaging but their full impact would not become clear for a week or more.

"I don't think it will be fatal but time will tell. The Liberals have high ground on the diversity and racism file, and Trudeau needs to unremittingly note how he screwed up ... Voters will then decide," Graves said.

Trudeau has championed racial equality and diversity as prime minister over the past four years, and he has three prominent ministers of Indian descent in his cabinet.

On Wednesday, Trudeau also admitted to performing "Day O", a traditional Jamaican song made famous by Harry Belafonte, in brown face during a high school talent show years earlier.

The Canadian Broadcasting Corp then published a picture from the performance that a Liberal spokeswoman confirmed as authentic.

Global News put out a video showing Trudeau again in dark make-up making faces and sticking his tongue out. It was not immediately clear exactly when that video was from.

"We can confirm that it is him and it's from the early 1990s," a Liberal official said.

Conservative Party leader Andrew Scheer, Trudeau's main rival, said that the video was proof that the prime minister had lied during his apology on Wednesday because he only mentioned having dressed in brown face twice.

"He did something that was racist and he lied about the extent of such activities," Scheer told reporters in Saint-Hyacinthe, Quebec.

But Scheer also acknowledged the Conservatives had leaked the video to Global News.

Australian Associated Press