VANCOUVER -- Protesters managed to evade security and disrupt a Vancouver event involving Prime Minister Stephen Harper on Monday.

Just as Harper was about to launch into a question-and-answer period put on by the Vancouver Board of Trade, two people carrying placards walked across the stage behind the prime minister.

The signs read: "Climate Justice Now" and "Conservatives Take Climate Change Seriously" with a black line through the sentence.

Board president Iain Black asked that the stage be cleared as the protesters stood behind the prime minister.

Harper quipped "it wouldn't be B.C. without it" to applause and laughter from the crowd.

"A warm British Columbia welcome," Black added as the prime minister smiled and chuckled.

The demonstrators were led off the stage and out of the room without a confrontation.

A group calling itself a collection of environmental and other protest groups put out a news release saying two protesters managed to make it past police to disrupt Harper's event.

Harper answered several questions posed by Black on issues ranging from the proposed Northern Gateway pipeline project to the state of the Canadian economy.

The prime minister said worldwide energy demand proves that it's in Canada's interest to diversify its energy market, but the government shouldn't endorse particular pipelines.

"In every one of these cases, whether it's energy or other kinds of mining projects, the government has always followed the best scientific and expert advice available to us."

Harper said his government won't approve projects unless they are in the economic interests of Canada and meet the highest standards of environmental protection.

Last month, a joint review panel recommended that the Northern Gateway project go ahead, but included more than 200 conditions.

Harper refused to say more about the multibillion-dollar line because the panel's report is before cabinet.

Black asked Harper about the challenges posed by First Nations treaty rights in developing resource projects.

He noted that Canada has the prospect of significant economic resource development in regions where aboriginal people are often the dominant populations.

"If handled correctly, this is an unprecedented opportunity for aboriginal people and their communities to join the mainstream of the Canadian economy."

Harper suggested progress won't be made in First Nations communities without giving them that opportunity.

"I encourage aboriginals leaders to look at these things, not just as opportunities to gain a revenue stream, but opportunities to have people working on these projects, to have aboriginal businesses providing services," he told the Vancouver crowd.

On the economy, Harper said he expects the country will be buffeted by the uncertainty of other economies around the world, but added he's more optimistic this year than he has been in the past.

"I see real evidence of growth taking hold in the United States. It's not going to be a boom, and there are certainly longer term challenges there, with fiscal and other situations, that are going to have to be addressed.

"But I do think that 2014 is likely to present some good opportunities for our country."