Some 1.5 million Finns have already cast their ballots during a week of advance voting this month.
Finns began voting in a general election on Sunday where the centre-right government is expected to be overturned amid widespread opposition to its spending cuts, and the far-right is predicted to make large gains.
As polling stations opened at 0600 GMT, Helsinki was typically quiet, and a trio of young women were the first to appear at the Normaalilyseo high school in the city centre to cast their votes.
A record 1.5 million Finns, over a third of the electorate, have already cast their ballots during a week of advance voting this month.
"After those who have voted in advance, we have about 1,700 people who have a right to vote today (in this district)," election official Vesa Hintsanen said at the school on Sunday.
Much of the debate in the run-up to the election has been about whether the next government should continue the current administration's public spending cuts.
The opposition Social Democratic Party, which Finland's main polls predict will win by a margin of about two percentage points, has vowed to alleviate the austerity policies introduced by the ruling coalition over the past four years.
Aware the public mood has turned against any further belt-tightening, the Centre Party of incumbent Prime Minister Juha Sipila and his centre-right governing partner the National Coalition Party, have insisted the economy is now strong enough to allow for an easing of austerity.
In recent months, Finland's far-right Finns Party – previously languishing in fifth place in opinion polls – has surged in popularity to become the second- or third-biggest party, according to recent forecasts.
The Finns Party focused its campaign on immigration, urging people to "Vote for some borders", and on climate change, where it denounced the "climate hysteria" of other parties and pledged that citizens should not have to pay for efforts to contain global warming.
Polling stations close at 1700 GMT, with a provisional vote count expected before midnight.
Governments in Finland are usually coalitions of three or four parties. The winner of most votes on Sunday will be tasked with heading negotiations to form a majority government.