He sounded somber, but firm as he told supporters that "now it is up the political parties to cooperate responsibly and create a strong government". "And the Social Democrats and a Social Democratic-led government is a guarantee for not letting the Sweden Democrats extremist party, racist party, get any influence". We must gather all forces for good. "We used to be a very calm nation", she said.
Lofven had urged Swedes not to vote for what he called a "racist party" as he cast his ballot on Sunday.
Akesson has said he would demand a curbing of immigration policy in exchange for his support, or key positions on parliamentary committees that draft legislation.
The far-right Sweden Democrats, who have capitalised on voters' frustration over immigration after the country welcomed nearly 400,000 asylum seekers since 2012, were seen making steady gains, rising from 12.9 per cent in 2014 to 17.7 per cent.
Final election returns were expected later in the week.
He and his wife Ulla - who lead the sort of simple, modest lifestyle seen as a virtue in Sweden - were recently featured in the pages of a celebrity magazine, and on television, an unusual move for a Social Democratic politician.
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". The center-right Moderate Party is set to take to take third place with 17.7 per cent.
Sweden's national election commission reported the governing Social Democrats had 28.1 percent of the vote at a little past the midway point in the vote count from Sunday's election.
To counter that he has taken a hard line, repeatedly stressing that new arrivals in Sweden have both "rights and responsibilities". With deadlock looming, it could take weeks to form a government.
This item has been corrected to show the ruling party represents the center-left, not center-right.More news: Pence Says He'd Sit Down For Mueller Interview
Acrimony between the two main political blocs has defined Swedish politics for decades, and the rise of the Sweden Democrats - long a pariah grouping in parliament - has hugely complicated the political landscape.
The poll projects that the ruling party received 26.2 percent of the vote.
Far-right parties have made spectacular gains throughout Europe in recent years after a refugee crisis sparked by civil war in Syria and conflicts in Afghanistan and parts of Africa. Moderate party secretary Gunnar Strommer said after the exit polls were published that he thinks "it's pretty clear" Lofven will have to resign.
The Svenska Dagbladet newspaper said the Nordic Resistance Movement members entered voting stations and attempted to take photos of voters, voting slips and journalists.
Svenska Dagbladet also reported that the far-right Alternative for Sweden party raised alleged election breaches by "shouting loud" on social media as soon as polls opened on Sunday.
"Integration is one of the biggest questions for the future in Sweden".
Seen by some as a poor orator who lacks charisma, he is nevertheless popular with many Swedes who see him as "genuine".
At the Swedish Democrat's election eve rally Saturday, party leader Jimmie Akesson criticized Lofven's government for "prioritizing" the needs of new immigrants the ones of Swedish citizens. He has insisted that he is still right about the general picture of the country as one where large-scale migration has brought security threats.
The latest opinion poll suggests that Prime Minister Stefan Lofven's ruling Social Democrats will substantially lose seats but still emerge a victor with an estimated 24.9 percent of the votes.
The Sweden Democrats, a party with white supremacist roots, rose to 19.2 percent from 12.9 percent in the previous election, the poll by public service broadcaster SVT suggested, depriving either of the mainstream blocs of a parliamentary majority.