Argentina's Peronists have swept back into power, ousting conservative president Mauricio Macri in an election result that shifts Latin America's third-biggest economy firmly back toward the left after it was battered by economic crisis.
Peronist Alberto Fernandez had 47.79 per cent of the vote ahead of Macri's 40.71 per cent with more than 90 per cent of ballots counted on Sunday night, putting the centre-left challenger over the 45 per cent threshold to avoid a runoff and win the election outright.
Macri, speaking at his election party, conceded the race and congratulated Fernandez. He said he had invited Fernandez to the presidential palace on Monday morning to discuss an orderly transition, which is seen as essential for Argentina's shaky economy and markets.
The president-elect said he would meet with Macri to discuss the transition, added that he would collaborate "in every way he could" to deal with the country's dire economic situation.
Raucous crowds cheered at Fernandez's election headquarters but the mood was far more muted across the city at Macri's election party, even though his "Together for Change" coalition performed much more strongly than many polls had expected.
A candidate needs 45 per cent of the vote, or 40 per cent with a 10-point lead over the runner-up, to avoid a second round.
Fernandez had been the heavy favourite since winning a landslide victory in primaries in August. He extended that lead in pre-election opinion polls.
The vote will have far-reaching implications. Argentina is one of the world's top grain exporters, is stirring the energy world with its huge Vaca Muerta shale field and is on the cusp of restructuring talks with creditors over $US100 billion ($A146 billion) in debt.
Australian Associated Press