TUNIS - Tunisian presidential candidate Beji Caid Essebsi's campaign manager told reporters he was ahead in Sunday's election by at least 10 points, according to his own party's initial results.

Official results have yet to be released by electoral authorities. But Essebsi and rival Moncef Markouzi, the incumbent, were expected to be frontrunners in the first free presidential election since Tunisia's 2011 uprising.

Political parties have observers at polling stations who act as witnesses to oversee preliminary counts, which allows them to tally results unofficially for their party.

Tunisians voted Sunday in their first presidential election since the 2011 revolution that sparked the Arab Spring, in a ballot set to round off an often fraught transition to democracy. The favourite among 27 candidates was former premier Beji Caid Essebsi, an 87-year-old veteran whose anti-Islamist Nidaa Tounes party won a parliamentary election last month.

Others vying for the presidency included outgoing President Moncef Marzouki, several ministers who served under ousted dictator Zine El Abidine Ben Ali, leftwinger Hamma Hammami, business magnate Slim Riahi and a lone woman, magistrate Kalthoum Kannou.

Whatever the outcome many Tunisians saw the election as a milestone in the history of the North African country, where for the first time they could freely choose their president. "This election is very important. It's the culmination of the revolution and something that we really should not pass up," said an electoral observer who gave his name only as Moez.

Bechir Yahyaoui could hardly control his emotions as he voted in the Tunis district of Hay el-Khadhra, saying that for once he was "voting for who I want, with no pressure, no bribes".

"Before (under Ben Ali) you had to go and vote, regardless of the outcome. This time the election is free and transparent," he said. But voting appeared slack and three hours after polling stations opened at 0700 GMT, officials estimated turnout at only 12 percent.

Some 5.3 million people were eligible to vote, with tens of thousands of police and troops deployed to guarantee security amid fears Islamist militants might seek to disrupt polling day.

Polling was restricted to just five hours in about 50 localities near the Algerian border, where armed groups are active, while polls elsewhere were due to close at 1700 GMT. A run-off vote will be held at the end of December if no candidate secures an absolute majority.

Prime Minister Mehdi Jomaa hailed the vote. "It's a historic day, the first presidential election in Tunisia held under advanced democratic norms," Jomaa

said. "God willing, it will be a great festival of democracy."

Tunisia has won international plaudits for largely steering clear of the violence, repression and lawlessness of other Arab Spring countries such as neighbouring Libya.

Until the revolution, Tunisia knew only two presidents -- Habib Bourguiba, the "father of independence" from France in 1956, and Ben Ali, who deposed him in a 1987 coup.

To prevent the emergence of another dictatorship, presidential powers have been restricted under a new constitution, with executive prerogatives transferred to a premier drawn from parliament's top party.

Frontrunner Essebsi ran on a campaign of "state prestige", a slogan with wide appeal to Tunisians anxious for an end to instability.

Supporters argue only he can stand up to the Islamists who first held power in the post-Ben Ali era, but critics charge he is out to restore the old regime, having served under both former presidents.

"Long live Tunisia," Essebsi said as he cast his ballot at a polling station in a Tunis suburb, where he was among the first to vote.

Marzouki, who has been hammering home the argument that he is the only leader capable of preserving the gains of the uprising, voted in the afternoon near the city of Sousse, south of Tunis.

A group of protesters demonstrated against his bid for re-election but were kept at bay by police, an AFP reporter said.

Critics have accused Marzouki of having forged a pact "with the devil" in 2011 when he joined a coalition with the moderate Islamist party Ennahda.

Ennahda, which came second in the parliamentary election, did not put up a candidate and invited its members "to elect a president who will guarantee democracy".

"The polls are an important turning point for Tunisia, the outcome of a whole process that will allow Tunisians to decide their future," said veterinary professor Jamel Shemli.

Whoever wins, tackling the faltering economy will be a top priority, with unemployment, a leading cause of the revolution, running at 15 percent.