RIO DE JANEIRO (Reuters) - Right-wing Brazilian President Jair Bolsonaro warned on Monday that his country could see a wave of migrants fleeing Argentina if a presidential election there returns leftist politicians to power, after their strong showing in a Sunday primary vote.

Bolsonaro has cast himself as foe to the left-wing leaders around Latin America and celebrated his friendship with Argentine President Mauricio Macri, who faces long odds of winning another term in October.

The Brazilian president singled out as a "leftist scoundrel" Argentina's former president Cristina Fernandez de Kirchner, the vice-presidential candidate on the ticket confirmed as front-runner on Sunday. He compared her to ideological allies from Cuban President Fidel Castro to Venezuelan President Nicolas Maduro.

Speaking in southern Brazil, Bolsonaro warned it could soon see migration on par with the north of the country, where waves of Venezuelans have fled an economic crisis.

"We don't want that: Argentine brothers fleeing over here, seeing how awful it could get if the result of the vote yesterday is confirmed in October," he said.

Argentina's peso currency collapsed on Monday and inflation was expected to rise as voters flirted with a return to interventionist economics by snubbing market-friendly Macri for the opposition in a primary vote on Sunday.

Bolsonaro's government has not been shy about weighing in on domestic politics around the region, antagonizing Venezuela's Maduro and touting a close friendship with Paraguayan President Mario Abdo when he faced the threat of impeachment.

Bolsonaro tapped his son Eduardo to become ambassador in Washington, citing praise from U.S. President Donald Trump. In a visit to Washington, Eduardo Bolsonaro met with members of the conservative movement and wore a cap emblazoned: "Make America Great Again - Trump 2020".

(Reporting by Pedro Fonseca; Writing by Brad Haynes; Editing by Alistair Bell)