Election surveys show that issues such as unemployment and corruption are prioritized during the Colombian presidential election.
The dissatisfaction last year led to major street protests in the country and several people died.
- The dissatisfaction has followed the election campaign and has meant that the established parties, which have dominated Colombian politics, have been eradicated from the political map, says SVT's correspondent Tigran Feilier.
Voters are now looking for new solutions to the country's problems and therefore the choice is between two "outsiders", he continues.
Growing gaps are causing voters to turn left
Colombia is one of the world's most unequal societies and the gaps between rich and poor have widened further.
Concerns about the future have given left-wing candidate Petro, whose support is particularly strong among young voters, air under their wings.
- He has pushed the climate issue in a clear way, but also other issues related to discrimination, racism and women's rights, where he has been strong in those groups.
"The second big surprise"
The challenger Rodolfo Hernández was until recently a relatively unknown mayor of a medium-sized Colombian city.
- He has expressed himself very controversially about Venezuelan immigrants and the role of women, including that women should not engage in politics but best stay at home, says Tigran Feiler.
The second round of elections will be held on 19 June.