Prime Minister Stephen Harper and Liberal Leader Michael Ignatieff have stopped attacking each other and are instead targeting New Democrat Leader Jack Layton, who presents a formidable challenge to both leaders according to recent polls.

During a campaign stop in Niagara Falls, Ont. on Thursday morning, Harper neglected to even mention Ignatieff -- who has been his primary target throughout the campaign -- instead taking aim at Layton.

Harper charged that Layton would turn back the clock on cross-border relations with the U.S., while the Conservatives would try to boost trade and improve security.

"The NDP has been Canada's most consistent, most vociferous and most aggressive opponent of a strong trading relationship with the United States," Harper said. "The NDP approach to issues like trade has not changed since the Cold War. It is an ideological throwback."

Harper also claimed that the New Democrats' cap and trade plan would push gas prices up by 10 cents per litre.

The change in tactics comes as surging NDP support threatens to derail Harper's drive for a majority Conservative government.

New poll numbers from Nanos Research put the NDP in first place in Quebec with the party enjoying around 30 per cent support nationally, a close second to the Conservatives at 36 per cent and eight points ahead of the Liberals.

The Conservatives are also launching attack ads targeting the NDP instead of the Liberals, who now face the prospect of being squeezed out in the May 2 vote as they lose momentum.

Speaking Thursday in Quebec, where the New Democrats now lead the Bloc Quebecois in the polls, Ignatieff warned that Canadians shouldn't mistake Layton's likability for an ability to run the country.

He said the NDP leader has gotten a free ride, because until now no one considered him a serious contender for leadership.

"He has a lovely smile," Ignatieff said. "But no one has put Mr. Layton under a microscope. I've been under a microscope for the last five years."

In a release issued Thursday the Liberals panned Layton's promise to tackle the immigration backlog, saying the party's platform doesn't explain how the NDP would fund such an initiative.

The almost daily "Reality Check" releases from the Liberals have also challenged Layton on statements about eliminating offshore tax havens, hiring 1,200 doctors and 6,000 nurses, and collecting revenue expected from a proposed carbon cap and trade system.

The Liberals say the unrealistic promises would result in "a trail of broken promises" if the NDP were to end up in government.

"We've gotta be clear on the Constitution, we've gotta be clear on culture, we've gotta be clear on the gun registry, it's the minimum condition for being a serious party in Canadian politics. We are clear, Jack Layton is not," Ignatieff said Thursday.

Layton: 'Winds of change' are blowing

Layton, riding high on his newfound success in the polls, challenged young people to vote during a campaign rally in Yellowknife, N.W.T. on Thursday.

"The winds of change are blowing across this country, and this time it's young people leading the way," Layton told a rally at candidate Dennis Bevington's office in Yellowknife.

"We're all counting on you to build the 21st-century version of Canada -- and lasting change starts with a vote."

While the Conservatives are still leading all of their rivals in national polls, the New Democrats have recently surfaced as their primary competition in many regions across Canada.

In Ontario, which houses nearly a third of all federal ridings, a prominent labour group pledged in a statement Thursday to "work tirelessly for the next five days" in the hopes of winning more votes for the party.

Citing the NDP's rising popularity, Ontario Federation of Labour president Syd Ryan wrote that "thousands of trade union activists" would be out canvassing in communities across the province.

Such momentum has given NDP Leader Jack Layton the confidence to begin dropping hints that the New Democrats could hold much greater power in Ottawa after this election, if the polls are accurate.

"As your prime minister," Layton began a speech in Winnipeg on Wednesday, prompting loud applause and cheers.

"Sounds like you like that phrase," the NDP leader said after being drowned out by the crowd. He then repeated it several times, each time being met by thunderous applause.

With files from The Canadian Press