The presidential candidate of the conservative coalition that has governed Uruguay for the past five years conceded defeat on Sunday after a close run-off election, even as the vote count continued.

Alvaro Delgado, the centre-right government's candidate, told supporters at his campaign headquarters that "with sadness, but without guilt, we can congratulate the winner," referring to left-wing challenger Yamandú Orsi.

Electoral officials said Orsi had secured 784,523 votes with over half of all ballots counted, compared with Delgado's 771,434.

Delgado's concession, with more than 57 per cent of official votes counted, ushers in Orsi of the centre-left Broad Front as Uruguay's new leader.

It spells an end to the short stint of the right-leaning government in Uruguay that in 2020, with the election of President Luis Lacalle Pou, had broken 15 years of rule by the Broad Front.

The Broad Front drew international acclaim over those years for overseeing the legalization of abortion, same-sex marriage and the sale of marijuana.

The party released a statement on X, formerly Twitter, saying "Joy will return" and announcing Orsi as president.

"I called Yamandú Orsi to congratulate him as President-elect of our country," Lacalle Pou wrote on X, adding that he would "put myself at his service and begin the transition as soon as I deem it appropriate."