Finland's opposition conservatives have taken a tiny lead in early results over Prime Minister Sanna Marin's centre left in Sunday's general election.

Almost 40% of voters cast ballots ahead of election day, and Petteri Orpo's National Coalition Party has won 20.8% of the vote so far.

Sanna Marin's Social Democrat Party is on 20.7%.

The election is seen as a three-way race and Riikka Purra's right-wing populists The Finns are close behind.

The Finns Party is on 18.6%, according to the results of some 1.7 million votes, and leader Riikka Purra says they are still fighting for first place.

Finnish commentators say the results could still swing between parties as the evening progresses.