It is one of the most open presidential elections in decades and taking place under the shadow of the South American country's worst economic crisis in 20 years.

The vote is likely to disturb Argentina's already-shaky markets, and impact its ties with trading partners.

Polling opened at 8am (11am GMT) with three frontrunner candidates likely to split the vote: libertarian economist Javier Milei, centrist Peronist economy minister Sergio Massa, and conservative Patricia Bullrich

Mr Milei, pledging to "chainsaw" the economic and political status quo, is the candidate to beat, with angry voters flocking
to his tear-it-all-down message, fed up with inflation at 138% and poverty affecting over two-fifths of the population.

Mr Milei, a brash former TV pundit likened to Donald Trump and Jair Bolsonaro, posted a shock win in August open primaries, though Mr Massa and Mr Bullrich were not far behind and it may prove a close race. Pollsters expect no outright winner.

A candidate needs more than 45% of the vote - or 40% and a 10-point lead, to avoid a second run-off, which would be held on 19 November.

The first results are expected around 9pm local time (midnight GMT) this evening.

What will the winner have to deal with?

Whoever wins will have to deal with an economy on life support: central bank reserves are empty, a recession is expected after a major drought, and a $44bn programme with the International Monetary Fund (IMF) is wobbling.

Amid this crisis Mr Milei has risen abruptly, pledging shock therapy to fix the economy including dollarizing, shutting the
central bank, reducing the size of government drastically and privatizing state entities.

Mr Massa, the current economy chief, is in the running despite overseeing inflation hitting triple digits for the first time
since 1991. He has pledged to cut the fiscal deficit, stick with the peso and defend the Peronist social welfare safety net.

Ms Bullrich, a former security minister who is popular in business circles, has seen her support diluted by the unexpected emergence of Mr Milei.