Libertarian outsider Javier Milei swept to victory in Argentina's presidential election Sunday, vowing to halt decades of economic decline in a country reeling from triple-digit inflation.

The self-described "anarcho-capitalist" pulled off a massive upset by ousting the populist Peronist coalition which has long dominated Argentine politics.

With 55.7 percent of the vote, Milei thumped his rival, Economy Minister Sergio Massa, who won 44 percent of the vote and rapidly conceded defeat.

"Today begins the reconstruction of Argentina. Today begins the end of Argentina's decline," Milei said in his victory speech. "The model of decadence has come to an end. There is no way back."

Latin America's third-biggest economy has suffered decades of crises under interventionist governments big on welfare that resort to printing money to finance spending, fueling inflation, while borrowing heavily only to default on their debt.

Access to dollars is strictly controlled, leading to a thriving black market for greenbacks, and analysts warn the peso is ripe for a sharp devaluation.

"There is no room for gradualism... or half-measures," said Milei.

Milei's main platform has been a plan to ditch the ailing peso for the US dollar and "dynamite" the Central Bank to do away with the "cancer of inflation."

Analysts, however, warn the country is too low on dollar reserves for the move to happen anytime soon.

"This is the change that us young people want. I am not afraid of Milei, I am afraid my dad won't be able to pay his rent. The Argentine peso isn't worth a thing," said Juan Ignacio Gomez, 17.

'I am not afraid' 

Thousands of Milei supporters waved flags and chanted "freedom" as they celebrated outside his campaign headquarters.

"We are tired of Peronism. Milei is an unknown, but better a madman than a thief," said 50-year-old writer Nacho Larranaga, wearing the blue-and-white Argentina flag as a cape.

Milei, a 53-year-old economist with wild hair and thick sideburns, has drawn comparisons with former US president Donald Trump and Brazil's Jair Bolsonaro for his abrasive style and controversial remarks.

Both former presidents congratulated him on social media.

US Secretary of State Antony Blinken said Washington "(looks) forward to working with President-elect Milei and his government on shared priorities."

Milei had vowed on the campaign trail to cut ties with his country's top trading partners Brazil and China, saying he would not "do business with communists."

Following Milei's victory, Brazil's President Luiz Inacio Lula da Silva wished "good luck and success" to the new Argentine government.

China said Monday it would continue working with Argentina, congratulating the president-elect on his victory.

"China has always attached great importance to the development of China-Argentina relations from a strategic and long-term perspective," foreign ministry spokeswoman Mao Ning said at a regular briefing.

Milei is against abortion, has insulted Pope Francis, questioned the death toll under Argentina's brutal dictatorship and says humans are not causing climate change.

He took to the stage in his campaign wielding a powered-up chainsaw to symbolize the drastic cuts he plans to make to a bloated state.

'The lesser evil' 

Milei's red-faced rants against the "thieving and corrupt political class" struck a nerve with Argentines struggling to make ends meet and fed up with politicians they see as the architects of their misery.

He carried out much of his campaign on TikTok and other social media, firing up young people.

Others were spooked by his style in an election that has polarized the nation.

Teacher Catalina Miguel, 42, among a dejected crowd at Massa's campaign headquarters said she was in "shock."

"Milei will find us on the street defending every right he seeks to challenge. Half of Argentina does not support him."

On the other end of Milei's chainsaw are millions of Argentines who depend on welfare assistance and generous government subsidies of fuel, electricity and transport -- with bus tickets costing only a few cents.

Meanwhile, the country's coffers are in the red, with $44 billion debt with the International Monetary Fund looming over the incoming government.

'Quick decisions' 

Political analyst Ana Iparraguirre said that Argentines should brace themselves.

"Whoever comes into office has to make some quick decisions that are going to hurt people."

As Milei is set to take office on December 10, leaving his rival Massa still in charge of the economy for three weeks, analysts predict a rocky ride with the strictly controlled peso ripe for devaluation.

Michael Shifter of the Inter-American Dialogue think-tank in Washington said Argentina "is part of the regional trend of a real weakening of political parties and the emergence of an outsider who... has a powerful message that resonates: just get rid of the political class and then everything will be ok."