Ms Fernandez won more than 50% of the vote - enough to win outright in the first round presidential election in October.

Battling for second place were former President Eduardo Duhalde and Radical Party Senator Ricardo Alfonsin.

In fourth place was the socialist provincial governor Hermes Binner.

The unified national primary - in which voting is obligatory - was designed to deepen Argentina's democracy by forcing all political parties to let voters choose their presidential candidates.

Instead, all 10 main parties announced single candidates, leading critics to describe the process as a mere dress rehearsal - or a very expensive opinion poll.

After casting her vote in the southern city of Rio Gallegos, President Fernandez hailed the primary as "historic" and a "qualitative leap" for Argentina.

"We are building a political system that is more transparent, more plural, and in which the people can express their opinion".

Favourite

Ms Fernandez, 58, was already the clear favourite to win a second term as president, when the election is held on 23 October.

She will need 40% to avoid a second-round run-off, as long as she also has a 10-point lead over her nearest challenger.

Otherwise, 45% is required to win outright.

It had been expected that Ms Fernandez's husband and predecessor as president, Nestor Kirchner, would bid to succeed her.

But he died of a heart attack last October at the age of 60, and in June Ms Fernandez confirmed she would seek re-election.

President Fernandez retains strong popularity, based largely on Argentina's strong economic growth, as well as her efforts to reduce poverty.

Supporters also credit her and her husband with steering Argentina out of a deep economic crisis a decade ago.

However, she has angered Argentina's farmers by increasing taxes and restricting exports.

Critics also accuse her government of deliberately understating the inflation rate.