The Social Democrat-led red-green group, which also includes the Green and Left parties, was tipped to get 44.8 percent of the vote, according to the poll by public broadcaster SVT, while the anti-immigration Sweden Democrats were on 10.5 per cent, doubling their vote from the last election four years ago.
The centre-right four-party coalition which has ruled Sweden for the past eight years was slated to get 39.7 percent, the exit poll indicated.
Loefven has campaigned on a promise to narrow a growing income gap that has many in traditionally egalitarian Sweden worried. He has also vowed to improve the educational system and spend more on infrastructure.
The result would be a major triumph for the Sweden Democrats and their 35-year-old leader Jimmie Aakesson, who has grown the party from a virtual non-entity less than a decade ago.
The party, which entered parliament for the first time in 2010, has tapped unease among many Swedes about a growing influx of refugees.
If he is now pushed out of power, it will reflect a yearning among the Swedes for change, after eight years with the same faces in power, say observers.
