Il Nuovo Postiglione - Jubilant Gustavo Petro elected Colombia's first leftist president

With more than 99.9 percent of votes counted, Petro -- the 62-year-old former mayor of Bogota -- held an unassailable lead of 50.45 percent compared to Hernandez's 47.3 percent.

"Today is a celebration for the people. Let's celebrate the first popular victory," Petro wrote on Twitter.

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 graft his main campaign pledge.

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

"May so much suffering be cushioned by the joy that today floods the heart of the Homeland. This victory is for God and for the People and their history," added Petro.

In another historic achievement, environmental activist and feminist Francia Marquez, 40, will become Colombia's first black woman vice president.

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

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.

- 'Dangerous' accusations of fraud -

Regional leftist leaders 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.

Diosdado Cabello, the second most powerful man in Venezuela, wished the new president "the greatest success," while Peru's President Pedro Castillo said Petro could "always count on" his country's support.

When voting in Bogota, Petro, who comfortably topped last month's first round, urged his supporters among Colombia's 39 million registered voters to "defeat any attempt at fraud with massive participation."

The national registrar, Alexander Vega, denounced such fears as "disinformation" while Hernandez, who voted in the northern city of Bucaramanga where he was mayor from 2016 to 2019, accused Petro of "creating an atmosphere of fraud."

Elizabeth Dickinson, Colombia analyst at the International Crisis Group in Bogota, told AFP such claims were "dangerous" and "could easily erupt into post-election unrest."

With the traditional political powers suffering a chastening first round defeat, many voters were wary about what the future would hold.

Alejandro Bueno, 20, an economics student in Bogota, said he hoped for "a peaceful transition to the next government."

- 'No clear mandate' -

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 percent of the country lives in poverty while 11 percent are unemployed.

"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, told AFP.

"This is a lesson that should be learned from Ivan Duque's administration, if Petro does not take a hard look in the mirror and think about how to govern with the other half of the country, we can expect four years of stalemate and brinksmanship."

One major worry for many is Petro's past as a radical leftist urban guerrilla 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 multi-faceted conflict, leaving many to fear what a Petro presidency would represent.

He has also vowed to negotiate with Colombia's last recognized Marxist guerrillas, 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)," said Dickinson.

E.Accardi--INP