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AFP
Daniel Scioli (left) and Mauricio Macri (right) will face each other in November
The two men bidding to be Argentina's next president have begun their campaigns for November's run-off vote.
The centre-right mayor of Buenos Aires, Mauricio Macri, surprised observers by securing almost as many votes as President Kirchner's chosen candidate, Daniel Scioli.
Mr Scioli's focus would be protecting jobs and welfare programmes, he said.
Mr Macri said he would address state spending 'abuses' and high inflation.
The candidate in third place, Sergio Massa, has not said who will get his backing in the second round.
President Cristina Fernandez de Kirchner was constitutionally barred from seeking a third term.
Electoral first
With 97% of the votes counted, Mr Scioli was ahead with 36.9% of the vote, while Mr Macri had 34.3%.
The result means Mr Scioli, governor of Buenos Aires province and a former world powerboat champion, will have to enter a run-off with Mr Macri on 22 November.
It is the first time an Argentine election will be decided by a second round.
"Today starts a new election campaign that will decide the future of Argentina," Mr Scioli told reporters.
He said the choice was between protecting industry, employment and social welfare, and what he called Mr Macri's proposal "to liberalise the market and take on debt".
Mr Macri, a former president of top football club Boca Juniors, said he would try to win over voters who did not choose him on Sunday.
"We will correct the abuses and the fraud of inflation,'' he said, referring to his campaign pledges to cut state spending and rein in the inflation rate, which officially stands at 14.5%.
Observers say a key role in the run-off campaign could be played by Sergio Massa, who came a distant third with 21.3% of the vote.
Mr Massa, a former ally turned rival of outgoing President Cristina Fernandez de Kirchner, has not said who will get his backing in the second round.
President Fernandez, who stands down after eight years in power, is constitutionally barred from seeking a third term.
Argentina elections: All to play for
14.5%
Official, but disputed, inflation level
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28.2% the inflation level in 2014, according to the World Bank
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0.7% amount IMF predicts the economy will shrink in 2016
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.