BBC- Argentine stock markets and its currency have both plunged after Conservative Argentine President Mauricio Macri suffered a shock defeat in primary elections on Sunday.
In early trading, Argentina’s main Merval stock index fell 32%, while the peso slumped 25% against the dollar.
Some of the country’s most traded stocks have lost one third of their value in just two hours.
Mr Macri’s loss has sparked fears of a change to the market-friendly regime.
There have been big drops in companies such as cement producer Loma Negra – down around 50% – and electricity distributor Pampa Energia which is off around 30%.
The presidential elections take place in two months’ time.
Left-wing candidate Alberto Fernández – who defeated Mr Macri in the primary – is now seen as the front-runner in presidential elections due in Octobe
His running mate is former president Cristina Fernández de Kirchner, who presided over an administration remembered for a high degree of protectionism and heavy state intervention in the economy.
Analysis by Daniel Gallas, BBC South America Business Correspondent
Argentina is a country that has suffered with all sorts of economic problems that are taught in textbooks.
But even by its standards, this market meltdown is unprecedented.
In just two hours, a third of the Merval index (which accounts for the most traded stocks in the country) was wiped out in value.
Investors are now pushing the “sell” button, as many believe it will be impossible for President Mauricio Macri to win the upcoming election in October.
If he loses, this will be the end of a pro-business agenda to save Argentina’s economy that has been implemented since Mr Macri came to power in 2015, which includes IMF loans, austerity measures and the end of capital controls.
Sunday’s primaries were seen as vindication for “Kirchnerismo” which have for years denounced Mr Macri’s plan as ineffective. The country is in recession and still suffering with inflation and poverty.
There are still two more months to go until the election – but few believe there will be surprises as big as this one coming up again.
Edward Glossop, from the London-based consultancy Capital Economics, said Mr Macri’s government could pull out all the stops to try to shore up popular support.
This could include easing budget curbs imposed as part of Argentina’s agreement with the International Monetary Fund.
“An outright loosening of the purse strings is possible. The IMF would probably turn a blind eye to this, since it is in its interest for President Macri to secure re-election,” he said, but added: “We doubt that these efforts would be enough to change voter perception.”
Argentina is currently in a recession and posted 22% inflation for the first half of the year, one of the highest rates globally.
Poverty now affects 32% of the population.