Hernandez, 77, accepted the result, in which he came up short by 700,000 votes, in a Facebook live broadcast.

“I hope that Mr Gustavo Petro knows how to run the country and is faithful to his discourse against corruption,” said the construction magnate, who had made fighting corruption his main campaign pledge.

Petro will succeed the deeply unpopular conservative Ivan Duque, who was barred by Colombia’s constitution from standing for re-election, in a country saddled with widespread poverty, a surge in violence and other woes.

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Speaking to delirious supporters at his party headquarters in Bogota, Petro held out an olive branch to his opponents.

“This is not a change to deepen sectarianism in Colombia. The change consists precisely of leaving hatred behind, leaving sectarianism behind.”

He added: “We want a Colombia that through its diversity is one Colombia”.

In another historic achievement for a country where 10 per cent of the population identify as Afro-descendants, environmental activist and feminist Francia Marquez, 40, will become Colombia’s first black woman vice-president.

“The great challenge that all of us Colombians have is reconciliation,” said Marquez, who was the target of threats during a fractious campaign.

“The time has come to build peace, a peace that implies social justice.”

In central Bogota, thousands of Petro supporters – mostly young people – rejoiced.

“I’m celebrating because finally we’re going to have change … this shows there is hope,” academic Lusimar Asprilla, 25, said.

Leftist leaders in the Latin America region were quick to congratulate Petro.

“Gustavo Petro’s victory is historic. Colombia’s conservatives have always been tenacious and tough,” Mexico President Andres Manuel Lopez Obrador wrote on Twitter.

“Joy for Latin America! We will work together for the unity of our continent in the challenges of a world changing rapidly,” tweeted Chile President Gabriel Boric.

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“The will of the Colombian people has been heard, it went out to defend the path to democracy and peace,” said Venezuela’s authoritarian President Nicolas Maduro, who has been branded a dictator by the opposition in his own country.

Meanwhile, US Secretary of State Antony Blinken sent congratulations to “the people of Colombia for making their voices heard in a free and fair presidential election”.

Amid fears a tight result could spark post-election violence, some 320,000 police and military were deployed to ensure security for the 39 million registered voters.

The electoral observer mission said one of Petro’s election monitors and a soldier were killed, both in the south.

Colombia is no stranger to political violence, with five presidential candidates having been murdered over the course of the 20th century.

Before the first round of this year’s presidential election, several candidates received death threats.

Petro will have to deal with a country reeling economically from the coronavirus pandemic, a spike in drug-trafficking related violence and deep-rooted anger at the political establishment that spilled over into mass anti-government protests in April 2021.

Almost 40 per cent of the country lives in poverty while 11 per cent are unemployed.

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“This result does not give the new president a clear mandate to execute his policy without at least trying to address concerns from his counterpart,” Sergio Guzman, president of the Colombia Risk Analysis consultancy, said.

Guzman said that unless Petro learns “how to govern with the other half of the country, we can expect four years of stalemate and brinkmanship”.

One major worry for many is Petro’s past as a radical leftist urban guerilla in the 1980s who spent almost two years in jail.

Left-wing ideology is intrinsically linked in many Colombians’ minds to the country’s six-decade long multifaceted conflict, leaving many to fear what a Petro presidency would represent.

He has also vowed to negotiate with Colombia’s last recognised Marxist guerillas, the National Liberation Army (ELN).

“To demonstrate he is not himself an extreme left wing politician, it would be very complicated for him to open negotiations (with the ELN),” Elizabeth Dickinson, Colombia analyst at the International Crisis Group in Bogota, said.

Additional reporting by Bloomberg