BUENOS AIRES - Buckling under the weight of an economic crisis, voters in Argentina gave Alberto Fernandez and his running mate, former President Cristina Fernandez de Kirchner, a victory in the presidential primaries on Sunday, dealing a setback on incumbent President Mauricio Macri.

With 58 percent of votes counted, Fernandez, who is running under Frente de Todos, received 47 percent of the vote, against Macri's 32 percent.

The official results have yet to be announced, but Macri has already acknowledged that he and his party, Juntos por el Cambio, had a "bad election".

"Tomorrow we'll have to redouble our efforts, to ensure that in October, we can continue with our change," said Macri referring to the general elections. He was flanked by his vice presidential running mate, Miguel Angel Pichetto, and other disappointed political allies.

The primaries are meant to settle internal battles in the parties, but they also act as a bellwether ahead of the October 27 polls.

The winner needs to achieve at least 45 percent or between 40 and 44 percent, and a 10-point lead over the nearest challenger, to win outright.

Failing that, voters will go to a runoff in November.

Voting is mandatory over the age of 18, and optional for people over the age of 70 and 16- and 17-year-olds. The official result was delayed more than an hour, with local media reporting failures in the software that scrutinise the votes.

This election is being fought on two key issues - the battered economy that has seen inflation skyrocket, the currency plummet in value, factories close and workers lose jobs.

Looming large is the presence of Cristina Fernandez de Kirchner's name in the ballot. She completed two terms as president, ushering in greater levels of social spending. Alongside her deceased husband, former president Nestor Carlos Kirchner, they built up a powerful left-wing political bloc known as Kirchnerismo.

By the time her term came to an end, allegations of corruption and a faltering economy dominated the conversation, and Macri eked out a win in 2015 on a promise of change. (FA)