Swedish Prime Minister Fredrik Reinfeldt on Monday praised the victory of his follow conservatives in Finland's weekend election but his foreign minister worried at the rise of the nationalist True Finns.

"Our sister party is now Finland's largest, proving that being responsible and managing the economy well is something voters reward," Reinfeldt, who heads Sweden's Moderates party, said in a statement.

The head of Finland's National Coalition Jyrki Katainen will almost certainly become prime minister after his party obtained the most seats, 44, in Sunday's vote, followed closely by the Social Democrats (SDP) with 42 seats.

But the True Finns saw a spectacular surge to 39 seats from only six in the previous legislature.

Swedish Foreign Minister Carl Bildt expressed dismay at the rise of the staunchly anti-European Union party.

"There is reason to be worried by the big gains of the nationalist populist in Finnish election. We wish a Finland that's Nordic and European (sic)," he said on his official Twitter feed.

On his official blog, Bildt said one worry was the True Finns' negative stance towards Swedish, which is one of Finland's official languages, spoken by only a small minority but an obligatory subject in Finnish schools.

Bildt's concern was echoed by Haakan Juholt, the new head of Sweden's main opposition Social Democrats, who said it was "worrying that a populist party that lacks ... social responsibility such as the True Finns has attracted such large electoral success."

Juholt however congratulated his follow Social Democrats, who beat all poll predictions of a poor showing in the Finnish vote, landing in second place.

The True Finns' rise was meanwhile welcomed by Sweden's own anti-EU party, the far-right, anti-immigration Sweden Democrats.

"We are thrilled that criticism of mass immigration and European supranationalism received such broad support in Finland," said Jimmie Aakesson, whose party last September surged in Swedish polls to enter parliament for the first time.

"The True Finns is a party which in many respects is similar to ours and I congratulate them on a very good election result," he added.