Nabil Karoui on Monday conceded defeat in Sunday's presidential election, issuing a statement of congratulations to his opponent Kais Saied, whom exit polls had earlier showed winning by a landslide. 

"I would like to congratulate you on your election to the presidency," Karoui said in a statement several hours before the electoral commission was expected to announce official preliminary results. 

Tunisia's electoral commission was expected to confirm Monday that voters gave conservative political outsider Saied a sweeping mandate to be the next president, thanks largely to young people who flocked to his side.  

In a contest that reflected Tunisia's shifting post-revolution political landscape, Saied, an independent, scooped up more than 70 percent of the vote, polls showed – sweeping aside his rival, charismatic media magnate Karoui. 

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With his three million estimated votes, Saied won double that of all 217 lawmakers combined who were elected in October 6 general elections.  

Official results were set to be announced at 7:00 p.m. (1800 GMT), according to the electoral commission ISIE, which reported turnout was at least 58 percent, a steep rise from the first round.   

Saied, a retired law professor with a rigid and austere demeanor that earned him the nickname "Robocop," was carried to victory by young voters, wooed by his anti-establishment platform.  

Around 90 percent of 18- to 25-year-olds voted for Saied, according to estimates by the Sigma polling institute, compared with 49.2 percent of voters over 60.  

In his first reaction, Saied thanked the country's young people "for turning a new page," and vowed to try to build "a new Tunisia."  

Thousands of people took to the streets of the capital Tunis late Sunday to celebrate Saied's victory, honking horns and singing the national anthem.