Beji Caid Essebsi has declared victory in Tunisia's presidential run-off vote, seen as the last step in a shift to full democracy four years after an uprising toppled long-time leader Zine El Abidine Ben Ali.

Official results are not due until Monday and his rival, the incumbent president, Moncef Marzouki, refused to concede defeat.

Soon after polls closed, Essebsi, an 88-year-old former parliament speaker under Ben Ali, announced that he had won by a clear margin and jubilant supporters took to the streets of the capital in celebration, chanting "Beji President!"

"There is a lot of anticipation in Tunisia. People are wanting to find out who won the elections," said Al Jazeera's Jamal Elshayyal, reporting from Tunis.

Notes from the field: Al Jazeera's Jamal ElShayyal in Tunis.

The turnout so far is still below 20 percent from what we are hearing from the election commission. However, it is expected to pick up as the day goes on. It is important to know that there are a number of factors that could result in a lower-than-expected turnout.

There is the fact that there is a bit of election fatigue, so to speak, as this is the third time that Tunisians are expected to go to the polls in less than two months.

There's also maybe some sense of fear in terms of the security situation after [an] ISIL video that was posted earlier that was threatening people not to take part in the election and threatening to attack institutions, although the government has tried their best to secure the polling stations and dispatch thousands of troops across [the country].

Victory for Essebsi would enable him to consolidate power, with his new secular party, Nidaa Tounes (Call for Tunisia), already controlling parliament after defeating the main Islamist party in legislative elections in October.

"I dedicate my victory to the martyrs of Tunisia. I thank Marzouki, and now we should work together without excluding anyone," Essebsi told local television.

But Marzouki's campaign manager, Adnen Monsar, dismissed the claim and said it was still too close to call.

"Nothing is confirmed so far," Monsar said.

The landmark second-round vote sets Tunisia apart from the turmoil of other Arab countries that went through uprisings that started in 2011 and were known by some as "the Arab Spring".

An hour before polls closed, election officials reported a turnout of 48 percent, suggesting voter fatigue in a country with about 5.3 million registered voters, voting for the third time in two months.

Turnout in the previous two contests was just under 70 percent of registered voters.

The election was held amid tight security and the closure of main border posts with strife-torn neighbour Libya and is considered Tunisia's first free presidential election since independence from France in 1956.

"This election doesn't interest me,'' said a young man sitting in a crowded cafe in front of a polling station in the capital Tunis' lower income neighbourhood of Yasmina.

"I voted before, but I feel the candidates lie. They promise to create jobs for the youth and improve living conditions, but they don't keep them.''

Essebsi, the favourite after taking 39 percent of the vote in last month's first round, has promised to restore the "prestige of the state'' after unrest and economic problems marked the years since the uprising.

"I voted for Beji Essebsi, because he has a lot of experience, and we have a lot of faith in him that he will fix the country," one supporter told Al Jazeera.

Marzouki, who took 33 percent of the vote last month, has warned that Essebsi, whose party also won October's parliamentary election, will bring back the authoritarian policies of previous regimes.

Tunisia's moderate Islamists, who still have a great deal of backing in the country, have not officially backed either candidate, but are believed to lean towards Marzouki.

Source: Al Jazeera and agencies