Finland's left-wing Prime Minister Sanna Marin conceded defeat on Sunday in the country's parliamentary election as the opposition right-wing National Coalition Party (NCP) claimed victory in a tightly fought contest.

The pro-business NCP was expected to win 48 of the 200 seats in parliament, narrowly ahead of the nationalist Finns Party with 46 seats and Marin's Social Democrats on 43 seats, justice ministry election data showed with all ballots counted.

"We got the biggest mandate," NCP leader Petteri Orpo said in a speech to followers, vowing to "fix Finland" and its economy.