The presidential candidate of the conservative coalition that has governed Uruguay for the past five years conceded defeat on Sunday after a tight run-off election.

The results means the South American nation joined others around the world in rebuking the incumbent party in a year of landmark elections.

Even as the vote count continued, Álvaro Delgado, the centre-right government’s candidate, told supporters at his campaign headquarters in the capital of Montevideo that “with sadness, but without guilt, we can congratulate the winner,” referring to left-wing challenger Yamandú Orsi.

Fireworks erupted over the stage where Orsi, 57, a working-class former history teacher and two-time mayor from Uruguay's centre-left coalition known as the Broad Front, claimed victory as crowds flocked to greet him.

“The country of liberty, equality and fraternity has triumphed once again,” he said, vowing to unite the nation of 3.4 million people after such a tight vote.

“Let's understand that there is another part of our country who have different feelings today," he said.

“These people will also have to help build a better country. We need them too.”

With more than 91 percent of the votes counted, Orsi had close to 50 percent support compared to Delgado’s 46 percent in an election in which nearly 90 percent of voters turned out, according to preliminary data released by the Electoral Court.

The rest were blank votes or non-voters.

While failing to entice apathetic young voters and generating extraordinary indecision, Uruguay's lacklustre electoral campaigns steered clear of the anti-establishment fury that has vaulted populist outsiders to power elsewhere in the world, like in the United States and neighbouring Argentina. (AP)