Canadians have gone to the polls - a day after prime minister Stephen Harper made a final appeal for a "strong, stable, Conservative majority government" and warned he could be toppled by a leftist coalition if he does not get it.
Mr Harper, in power since 2006, has won two elections but never with a majority of Parliament's 308 seats.
If he does not get a majority this time, opposition parties are expected to try to form a coalition government.
Until last week, most polls indicated Canadian voters would give the Conservative government another mandate, but recent polls show a late surge for the left, which could redraw Canada's landscape and leave Mr Harper out of a job.
The unexpected gains for the New Democratic Party have upended previous soundings that predicted the Conservatives would get enough votes for a minority mandate - or even win a majority.
Now a new scenario has emerged in which the New Democrats and the Liberals together win enough seats to form a New Democrat-led coalition.
New Democrat leader Jack Layton, whose party has socialist roots, said: "We can change the government. We're not just going to oppose Mr Harper, we're going to replace him."
Polls show the race has tightened between the Conservatives and the New Democrats, something no one predicted just weeks ago.
Ekos, a private polling company, gave the Conservatives 34.6%, the New Democrats 31.4% and the Liberals 20.4%. A series of other polls have reported similar results.
Nelson Wiseman, a professor at the University of Toronto, said of what has been dubbed the "orange wave" of New Democrat support due to the party's colour: "It's a complete shocker."