Sweden's center-left opposition bloc has taken the lead and could be on course to return to power, according to early results from Sunday's parliamentary elections.

The bloc is led by Social Democratic Party leader Magdalena Andersson. The early results suggest that the former prime minister is poised for a political comeback.

Her main challenger, conservative Prime Minister Ulf Kristersson of the Moderate Party, had been seeking a second four-year term and had pledged to bring the far-right Sweden Democrats into government.