Justin Trudeau is congratulated by his mother Margaret after the Liberal victory. Photo: BBC

The centrist Liberals, led by Justin Trudeau, started the campaign in third place but in a stunning turnaround now command a majority.

Mr Trudeau, the 43-year-old son of late Prime Minister Pierre Trudeau, said Canadians had voted for real change.

Incumbent Conservative PM Stephen Harper accepted defeat and his party said he will step down as leader.

It was the longest campaign in Canada's history, and had been thought to be much closer.

Speaking after the polls closed, Mr Harper said he had already congratulated Mr Trudeau, saying the Conservatives would accept the results "without hesitation".

Addressing his jubilant supporters shortly afterwards, Mr Trudeau said that Canadians "sent a clear message tonight - it's time for a change".

"We beat fear with hope, we beat cynicism with hard work. Most of all we defeated the idea that Canadians should be satisfied with less.

"This is what positive politics can do," he said, also praising Mr Harper for his service to the country.

Few had predicted a Liberal victory on this scale. They look set to win 184 out of 338 seats - 14 more than they need for a majority.

That represents a huge increase from only 36 that they had held after suffering their worst-ever election result in 2011.

They become the first party ever to move from third place in parliament to a majority in one election in Canada's history.

The Liberal Party's election platform included:

• Cutting income taxes for middle-class Canadians while increasing them for the wealthy
• Running deficits for three years to pay for infrastructure spending
• Doing more to address environmental concerns over the controversial Keystone oil pipeline
• Taking more Syrian refugees; pulling out of bombing raids against Islamic State while bolstering training for Iraqi forces
• Legalising marijuana

Meanwhile, the left-leaning New Democratic Party (NDP) is on course to win 44 seats, less than half the number they held in the outgoing parliament.

"I congratulated Mr Trudeau on his exceptional achievement," said NDP leader Tom Mulcair.

Conservative Party supporters had little to celebrate. Photo: ReutersThe New Democratic Party - which finished second in the 2011 elections - is now a distant third. Photo: Reuters

As the results began pouring in, former Conservative Justice Minister Peter MacKay said: "A sea of change here. We are used to high tides in Atlantic Canada. This is not what we hoped for."

It was a sweeping victory that seemed unthinkable five years ago, improbable just months ago and unlikely even a few days ago.

And yet shortly after midnight on Tuesday, Justin Trudeau took the stage at Liberal headquarters as prime minister elect.

When Mr Harper first announced that this year's general election campaign would be a record 78 days long, conventional wisdom was it would benefit the Conservatives, giving them more time to bring their financial advantages to bear.

In hindsight, however, the lengthy campaign gave Mr Trudeau an opportunity to introduce himself to Canadians and overcome conservative attacks that characterised the 43-year-old former high-school drama teacher as too inexperienced to lead the Canadian nation.

Mr Trudeau also successfully outmanoeuvred the New Democratic Party, campaigning to that party's left on economic issues.

For Mr Trudeau, the hard work of bringing the Liberal Party back from the ashes is over. Now, as the next prime minister of Canada, the even harder work of governing is about to begin.

Mr Trudeau campaigned on a promise of change, urging voters ahead of the polling day to "come together as a country".

Mr Trudeau's charismatic father, Pierre, is considered the father of modern Canada.

Mr Harper, 56, portrayed himself as the steady hand who could steer Canada's troubled economy back on track.

His campaign ran TV advertisements saying that Mr Trudeau was "just not ready" to take office.