HELSINKI (AFP) - Finns voted on Sunday (Jan 28) and are expected to re-elect president Sauli Niinisto who is credited for maintaining a balanced relationship with powerful neighbour Russia at a time of simmering tensions between Moscow and the West.

Polling stations opened at 0700 GMT (3pm Singapore time), and are set to close at 1800 GMT on Sunday (2am Monday Singapore time) for Finland's 3.5 million registered voters.

The latest opinion polls credited Niinisto with between 51 and 63 per cent of votes, having lost ground but still far ahead of the seven other candidates. His main rival, Pekka Haavisto of the Green party, was forecast to garner around 13-14 per cent support.

Niinisto needs at least 50 per cent of votes to win Sunday's first-round vote to be re-elected for another six-year term and avoid a second round of voting on Feb 11.

If he succeeds, it would be a first since Finland introduced a two-round presidential election by popular vote in 1994.

"It has become less clear whether he will win in the first round but everything indicates that in the end he will be re-elected as president," Teivo Teivainen, professor of global politics at the University of Helsinki, told Agence France-Presse.

Finland's most popular president in more than three decades, the 69-year-old who campaigned as an independent has skilfully shifted the EU member state closer to NATO without antagonising Russia, with whom the Nordic country shares the longest border in the bloc.

During his first term, Niinisto has meticulously cultivated ties with Russian President Vladimir Putin, who has been at odds with the West particularly since Russia's 2014 annexation of Crimea.