President Mauricio Macri has congratulated Jair Bolsonaro for his stunning victory in Brazil's second-round run-off, saying he is ready to "work together" with the president-elect.
Minutes after the result was confirmed by official data, Macri used Twitter to send his greetings to the triumphant Social Liberal Party (PSL) candidate, who will succeed Michel Temer as president in Argentina's giant neighbour.
Bolsonaro, the outspoken far-right congressman who has been criticised for his use of misogynistic, homophobic and racist rhetoric, saw off Fernando Haddad as expected on Sunday night in nationwide ballot, taking just over 55 percent of the vote, compared with just under 45 percent for the Workers' Party candidate.
In his congratulatory tweet, Macri added: "Congratulations to Jair Bolsonaro for the triumph in Brazil! I hope to work together for the good of the relationship of our countries and the well-being of Argentines and Brazilians."
From the White House, US President Donald Trump also pledged to work with Bolsonaro.
White House spokeswoman Sarah Huckabee Sanders said that Trump had congratulated the president-elect and that "both expressed a strong commitment to work side-by-side to improve the lives of the people of the United States and Brazil."
Chile's President Sebastian Piñera also used Twitter to send praise to Brazil, saying: "I congratulate the Brazilian people for a clean and democratic election."
Piñera tweeted Bolsonaro directly to say: "I am sure we will work with vision and strength toward a future that will favour integration and the welfare of our people."
Colombian President Iván Duque also used Twitter to send congratulations to the "democratically elected" president elect, saying he wished to "strengthen political, commercial and cultural ties."
Some regional reactions, however, were less warm.
The Venezuelan government of President Nicolás Maduro offered a formal reaction in which he extended "his sincere congratulations to the People of the Federal Republic of Brazil, on the occasion of the civic celebration of the second round of elections ... in which the candidate Jair Bolsonaro was elected as president of this South American country."