Polls open in Sweden after heated election campaign centered on immigration

An election official casts a voter's ballot at a polling station in Stockholm on Sunday.

(CNN)Polls have opened in Sweden's general election Sunday in one of the tightest contests the Scandinavian country has seen for decades as voters split over attitudes to immigration.

The far-right is expected to make substantial gains after a heated campaign dominated by the immigration issue, with most opinion polls showing that no single party is expected to win the vote outright.
Once a nation that welcomed refugees in high numbers, immigration has become a hot-button issue in Swedish politics following the mass migration of refugees to Europe in 2015, at the height of the Syrian war, when Sweden took in more than 160,000 asylum-seekers.
    The Swedish government, led by the center-left Social Democrats in a coalition with the Green Party, has since then hardened its policies on asylum-seekers and closed its southern border with Denmark to stem the flow of migration.
    The far-right Sweden Democrats, which have roots in the neo-Nazi movement, have capitalized on tensions that have arisen since the influx of refugees and have already seen a dramatic rise in support, polls show.
    Sweden Democrats leader Jimmie Akesson campaigns in Stockholm in Saturday.
    "I am concerned because I think that integration is an important issue. But I'm not sure about the way of the Sweden Democrats," voter Tuva Sundh told CNN after casting her vote. "I think it's healthy to have debate. But I do think it's become too heated in this election."