(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.
"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."
Sweden has had a succession of recent coalition and minority governments, but like in many European elections, the vote has been further splintered, increasing the likelihood of a hung parliament.
"I think we are facing an extremely complicated process to form a government, maybe the most complicated in modern times," political scientist Niklas Bohlin from the Mid Sweden University told Reuters news agency.
The Social Democrats have tried to appease anti-migrant sentiment in the country by urging more integration programs and resources for refugees in marginalized communities, and to help them access education.
The center-right Moderates have pledged to give more funds to the police, and are pushing for Swedish migration policy to fall in line with laws in other EU countries, such as Denmark and Germany. This would mean that migrants won't be able to stay unless they can prove that they can support themselves, enabling them to get a permanent residence permit.
They are also looking at ways of more quickly incorporating migrants into the workforce, such as promoting "simple jobs," a reference to work that can be obtained with only an elementary education.
Some 7.5 million Swedes are eligible to cast a ballot Sunday. Voting ends at 8 p.m. local time (2 p.m. ET), after which a state exit poll will forecast results and a real count of the votes will begin.