An exit poll is projecting that nearly one in five Swedish voters backed an anti-immigrant party with white supremacist roots in the Scandinavian country's election.
However, Swedish broadcaster SVT said its poll from Sunday's election indicates that the centre-left Social Democrats governing Sweden now would remain the largest party in parliament.
The poll projects that the ruling party received 26.2% of the vote.
If the exit poll results carry over to the official count, the far-right Sweden Democrats would be the second-largest party in parliament.
The poll gave the party 19.2% of the vote.
The Swedish government allowed 163,000 migrants into the country with a population of 10 million in 2015.
The number was far lower than the asylum-seekers Germany accepted that year, but the highest per capita of any European nation.
Ahead of the election, promising prospects for the Sweden Democrats had many Swedes worried about an erosion of the humanitarian values that have long been a foundation of their country's identity.
"This election is a referendum about our welfare," Prime Minister Stefan Lofven said.
"It's also about decency, about a decent democracy... and not letting the Sweden Democrats, an extremist party, a racist party, get any influence in the government."
About 7.5 million voters were eligible to choose the next members of the 349-seat Riksdag, or parliament.
About 6,300 candidates sought the four-year terms.
It was unlikely any single party would secure a majority of 175 seats.
The Sweden Democrats - led by Jimmie Akesson - have worked to soften their neo-Nazi image while helping to break down longstanding taboos on what Swedes could say openly about immigration and integration without being shunned as racists.
During a heated debate among party leaders on Friday, Mr Akesson caused a stir by blaming migrants for the difficulties they often have in finding employment and not adjusting to Sweden.
The broadcaster that aired the televised debate, SVT, afterwards called his remarks degrading and against the democratic mandate of public broadcasting.
Mr Akesson responded that state television should not take sides, and later announced that he would not take part in any of SVT's election programmes on Sunday.
At the party's rally on Saturday, he strongly criticised Mr Lofven's government for "prioritising" the cause of immigrants over the needs of citizens.
"This government we have had now, they have prioritised, during these four years, asylum-seekers," Mr Akesson said, giving an exhaustive list of things he says the government has failed to do for Swedish society because of migrants.
