Argentina goes to polls in first ever presidential run-off
Voting in Argentina's first ever presidential run-off - the first in the country's history - has started after neither presidential candidate managed to win the initial vote outright.
Daniel Scioli, the governor of Buenos Aires province, is up against Mauricio Macri, the city's mayor.
On the eve of the vote, centre-left candidate Mr Scioli lagged behind his centre-right rival in the polls.
Mr Scioli was marginally ahead in the first round, with 36.7% to 34.5%.
But under Argentinian law, a presidential candidate needs 45% of the vote or a minimum of 40% with a 10-point lead over the nearest rival to win outright.
Both candidates have been back on the campaign trail in the month since the first round. Sunday's vote marks the first time a presidential election in Argentina has gone to a second round.
At the scene: Wyre Davies, BBC News, Buenos Aires
Voting at several stations we saw around the capital appeared to be brisk, with a significant number of elderly voters patiently waiting to fulfil their civic duty.
Although in political and purely numerical terms, the city and province of Buenos Aires are the most important electoral regions in the country, both candidates - Daniel Scioli and Mauricio Macri - have made efforts to garner those extra few votes that could be so important in provincial towns away from the capital.
It is not quite the straightforward, clear choice between a pro-state and pro-private sector candidate sometimes portrayed in the media. Neither Mr Scioli nor Mr Macri are quite the demons they're portrayed to be by each others' camps and neither man will have the political or economic freedom to live up to his election promises.
Nonetheless, this is a very important day in Argentina and it could represent a break with more than a decade of paternalistic, populist government that has been such a feature of life under Cristina Fernandez de Kirchner.
Mr Scioli, a close ally of current President Cristina Fernandez de Kirchner, had been expected to win by a greater margin in October.
A member of President Fernandez's Front for Victory party, he was handpicked by the outgoing leader, who cannot seek a third term.
Since 2007 Mr Scioli has been governor of Buenos Aires province, considered one of the most influential posts in Argentine politics. Before that, he was vice-president to the country's late former leader and Ms Fernandez's husband, Nestor Kirchner.
The son of one of Argentina's richest men, Mr 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.
He leads the conservative Cambiemos (Let's Change) coalition.
Whoever wins the presidency faces significant economic challenges.
While the country gained strength after a financial crisis in 2002, its economy, the third-largest in Latin America, has slowed in recent years, with GDP growing by only 0.5% last year.
The government is also locked in a battle against American hedge funds who disagree with how it wants to restructure $100bn (£65bn) of debt on which it defaulted in 2001.
While the firms successfully sued Argentina for repayment, Ms Fernandez refused to pay.