Ulf Kristersson, leader of the Moderate Party and Stefan Lofven, leader of the Social Democratic Party during a party duel broadcast by Sweden's tv-channel TV4 from Linkoping, Sweden September 8, 2018.
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, born as a far-right political movement and now an anti-immigration party, garnered a little under 18% of the vote.
The nationalist Sweden Democrats scored 19.1 percent, well above the 12.9 percent they won in the previous election in 2014.
The new government, which could now take weeks to form, will need either cross-bloc alliances between centre-right and centre-left parties, or an accommodation with the Sweden Democrats, long shunned by all the other parties due to their extremist roots, to pass legislation - potentially giving the populists a say in policy.
Sweden's anti-immigrant far-right made gains in legislative elections Sunday and vowed to exert "real influence" as kingmaker, after both the left-wing and center-right blocs failed to obtain a majority and the make-up of the next government remained up in the air.
The record levels of asylum seekers in 2015 magnified worries about a welfare system that many voters already believe is in crisis, even though refugee numbers have fallen sharply since then.
The potential of a surge by the party had many Swedes anxious about an erosion of the humanitarian values that have always been a foundation of their country's identity.
Prime Minister Stefan Lofven stumped Saturday for his party, the Social Democrats, while portraying the Sweden Democrats as racist.
Nevertheless, their leader Jimmie Akesson told a party rally: "We will gain huge influence over what happens in Sweden during the coming weeks, months and years".
The other of the two blocs that have defined Swedish politics for a decade, the four-party center-right Alliance coalition, trailed close behind on 38.5 percent.
A partial tally of the vote by the Election Authority is due between 2000 and 2100 GMT. "We need tight responsible immigration policies". Far-right candidates and parties have seen their stock rise in Italy, Poland, Germany and elsewhere in the past year.
On a good night for the smaller parties, the ex-communist Left almost doubled its score to 9.8% and the centre-right Centre and Christian Democrat parties both advanced.
The leader of Sweden's Liberal Party, Jan Bjorklund, reiterated his rejection of any cooperation with SD.
He says he is interested in cooperating with other parties and wants to tell the head of the party that came in second, the Moderates, "how to govern the country". "They can't adjust to Sweden, and it's hard for them to get a job".
The Social Democrats and its allies 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.
Sabina Macri, voting in central Stockholm, said the current political situation has left her questioning her future in Sweden.