Markets panicked as the peso closed at 57.30 to the dollar, a drop of 18.76 per cent from its Friday closing figure, while the Merval index crashed 38 percent by close.
Pro-business President Mauricio Macri predicted worse would follow after Argentina's peso and the Buenos Aires stock exchange plummeted Monday following his crushing defeat by populist candidate Alberto Fernandez in a party primary election.
Markets panicked as the peso closed at 57.30 to the dollar, a drop of 18.76 per cent from its Friday closing figure, while the Merval index crashed 38 per cent by close.
On the New York stock exchange, Argentine bonds lost around 20 per cent and shares in companies from the recession-hit South American country haemorrhaged more than 50 per cent.
"This is just a taste of what's going to happen" if the Peronist Fernandez, whose running mate is corruption-tainted former president Cristina Kirchner, comes to office, Macri warned.
"This is about the past, there's a ton of people who don't keep their money in this country, who are leaving this country. It's incredible what could happen."
Ever since taking office, Macri has blamed Argentina's economic woes on the policies enacted by three successive Kirchner governments -- Cristina Kirchner's 2007-15 time in office was preceded by a single term for her late husband Nestor.
"We cannot go back to the past because the world sees this as the end of Argentina," said Macri.
"The Kirchnerist alternative has no credibility in the world."
Macri called a meeting with Central Bank president Guido Sandleris before the markets opened on Monday.
The Central Bank bought $50 million in pesos to try to halt the slide, but to no avail.
Speaking before the worst of the day's losses were known, Fernandez blamed the market reactions on government policies.
"The president cannot have peace of mind. The markets are giving warning that the government has put itself in a position it cannot respond to," Fernandez told Radio 10.
On Sunday, centre-right Macri was dealt a huge blow in his bid for re-election in October when he polled 15 points less than centre-left candidate Fernandez.
Argentina is currently in a recession and posted 22 per cent inflation for the first half of the year -- one of the highest rates in the world.
Poverty now affects 32 per cent of the population.
Backed by the International Monetary Fund, Macri has initiated an austerity plan that is deeply unpopular among ordinary Argentines, who have seen their spending power diminished dramatically.
The peso lost half its value against the dollar last year.
But the Buenos Aires stock exchange shot up eight per cent on Friday amid expectation that Macri would do well in Sunday's vote.
Those hopes were quickly quashed as it lost 10 per cent when operations opened on Monday, before plunging further throughout the day.
The worst-hit shares lost almost 50 per cent of their value.
Macri now faces a daunting task of trying to overturn a huge deficit in just two and a half months.
"The vote shows a profound dissatisfaction with the economic situation (and) the worry within society that the government is disconnected from reality and wasn't up to tackling the problems," political analyst Carlos Fara told AFP.
Worst political crisis'
Macri managed only 32 per cent in the party primaries, which that effectively acted as a nationwide pre-election opinion poll as all of the South American country's major parties had already chosen their presidential candidates.
"We've had a bad election and that forces us to redouble our efforts," said Macri, whose popularity has plunged since last year's currency crisis and the much-criticized $56 billion IMF bail-out loan he secured.
Political analyst Sergio Berensztein described it as the government's "worst political crisis."
Fernandez scored 47 per cent and if he repeats that result in the October 27 general election first round, he would win outright without need for a November 24 run-off.
Argentina's electoral law requires a candidate to gain 45 per cent for outright victory, or 40 per cent and a lead of at least 10 points over the nearest challenger.
"We always fix the problems that others create," said Fernandez to thousands of cheering supporters in Buenos Aires on Sunday night.
Analyst Rosendo Fraga said Macri and Fernandez need to come to a bipartisan "governability agreement," otherwise "it's going to be very difficult to build confidence" in the markets between now and October's vote.