Swedes vote on Sunday in a tight election dominated by fears over asylum and welfare, with the populist, anti-immigration Sweden Democrats vying to become the biggest party in a country long seen as a bastion of economic stability and liberal values.

Far-right parties have made spectacular gains throughout Europe in recent years following a refugee crisis sparked by civil war in Syria and ongoing conflicts in Afghanistan and parts of Africa.

In Sweden, the influx of 163,000 asylum seekers in 2015 has polarized voters, fractured the political consensus and could give the Sweden Democrats, a party with roots in the neo-Nazi fringe, a veto over which parties form the next government.

"Traditional parties have failed to respond to the sense of discontent that exists," Magnus Blomgren, a social scientist at Umea University.

"That discontent maybe isn't directly related to unemployment or the economy, but simply a loss of faith in the political system. Sweden isn't alone in this."

The center-left bloc, uniting the minority governing Social Democrat and Green parties with the Left Party, is backed by about 40 percent of voters, recent opinion polls indicate, with a slim lead over the center-right Alliance bloc. 

The Sweden Democrats, who want the country to leave the European Union and put a freeze on immigration, have about 17 percent, up from the 13 percent they scored in the 2014 vote, opinion polls suggest.

But their support was widely underestimated before the last election and some online surveys give them as much as 25 percent, a result that would likely make them the biggest party, dethroning the Social Democrats for the first time in a century.

With an eye on the European Parliament elections next year, Brussels policymakers are watching the vote in Sweden closely, concerned that a nation with impeccable democratic credentials could add to the growing chorus of euroskepticism in the EU. Sweden took in more asylum seekers per capita than any other country in Europe in 2015, magnifying worries about a welfare system that many voters already believe is in crisis.

Lengthening queues for critical operations, shortages of doctors and teachers and a police service that has failed to deal with inner-city gang violence have shaken faith in the "Swedish model," built on a promise of comprehensive welfare and social inclusion.

Sweden Democrats leader Jimmie Akesson has labeled the vote a choice between immigration and welfare. 

He has also promised to sink any government that refuses to give his party a say in policy, particularly on immigration. 

Mainstream politicians have so far rebuffed him.

Polling stations open at 0600 GMT and close at 1800 GMT, with exit polls set to be published by Sweden's two main broadcasters around that time. Results from the vote count will become clear later in the evening. 

(Top image: Sweden Democrats party leader Jimmie Akesson speaks during an election campaign event in Stockholm, Sweden, Sept. 8, 2018. /VCG Photo)