Canadians are casting their votes in one of the country's most unpredictable elections ever, one that could give the ruling Conservatives a more solid grip on power or, just as easily, force them out of office.
The right-of-center Conservatives, who have governed Canada since early 2006, started the campaign with a healthy lead and said they needed a majority of seats in the House of Commons to let them focus on the economic recovery and keep taxes low.
Over the last two weeks, Prime Minister Stephen Harper has watched his advantage dwindle in the face of an extraordinarily effective campaign by the left-leaning New Democrats, a pro-labor party that has never held power in Canada.
The death of Osama Bin Laden could give a last-second lift to the Conservatives, the party that has staked most on defence and security.
The NDP, which has deep anti-military roots, wants to pull Canadian forces out of Afghanistan immediately.
Much will depend on whether the New Democrats, whose organisational structure is weaker than that of the Conservatives or the Liberals, can get its supporters out.
I want you to create line-ups at the polls, my friends, because we can defeat Stephen Harper," party leader Jack Layton told he told a rally on Sunday.
Opinion polls show that the Conservatives will have the most seats in the new Parliament.
But if they do not have a majority, they can only govern with support from other parties, as has been the case since 2006.
The Conservatives currently hold 143 of the 308 seats in the House of Commons.
The last polling stations close at 7pm (3am Irish time) in the Pacific province of British Columbia, and exit polls are likely to tip a final result soon after that.
The New Democrats promise to increase corporate taxes, limit the interest charged on credit card balances and introduce a cap and trade system to curb the greenhouse gases blamed for global warming.
Harper says anything other than a Conservative victory would be economic disaster at a time when Canada,the largest single supplier of energy to the US, is recovering nicely from the global crisis.
A three-day rolling poll by Nanos Research late on Sunday put public support for the Conservatives at 37.1% with the New Democrats at 31.6%. The Liberals, who started the campaign in second place, were at 22.5%.
The New Democrats and the Liberals are competing for the same center-left voters and if they split the vote, the Nanos poll shows the result could mean a narrow majority for Harper. That would ensure him a fixed four-year term in power.
An Ekos poll, also released late yesterday, said the result would be much closer. It had the Conservatives at 33.9%, the New Democrats at 31.2% and the Liberals at 21.0%. No opinion polls are allowed on election day.