Conservative Mauricio Macri has been confirmed as the winner in Argentina's presidential elections after his ruling party opponent conceded.

With almost all votes counted, Macri led Daniel Scioli by 51.5% to 48.5%.

He danced on stage at a victory rally at his Buenos Aires headquarters and thanked his staff for their support.

Macri's victory is the first in more than a decade for Argentina's centre-right opposition and ends the 12-year rule of the Peronist Party.

"Today is a historic day," said Macri, addressing thousands of cheering supporters. "It's the changing of an era."

Sunday's victory completes a turnaround for Macri, who is currently mayor of Buenos Aires, after he lost in the first round of voting to Scioli.

But Scioli, who is the governor of Buenos Aires province, did not command enough of a lead to win the vote outright, forcing a run-off - the first in the country's history.

Macri went into Sunday's vote with a comfortable lead in opinion polls, and campaigned on pledges to bring new investment into the ailing economy, tackle crime and fight corruption.

The son of one of Argentina's richest men, Macri had a long career in business before entering politics.

In 1991, he was kidnapped and kept captive for 12 days by a gang of corrupt policemen demanding millions in ransom.

Four years later, he became president of Boca Juniors Football Club and used his success at the club as a springboard for his political career.

Scioli, a close ally of outgoing President Cristina Fernandez de Kirchner, had been expected to win by a greater margin in October.

He tried to regain momentum before Sunday's runoff by attacking Macri's market-driven economic policies as a throwback, but failed to regain a lead in the polls.