Sunday's vote represents the final stage in Tunisia's democratic transition nearly fours years after the autocrat Zine El-Abidine Ben Ali was ousted.

With a new constitution and full parliament elected in October, the north African state has been hailed as an example of democratic change in a region still reeling from the Arab Spring revolts.

The two candidates in the presidential race are Beji Caid Essebsi, leader of the anti-Islamist Nidaa Tounes party, and incumbent Moncef Marzouki (photo), who held the post through an alliance with the moderate Islamist movement Ennahda.

In the first round of voting in late November, a record 27 candidates entered the race, however, none of them won a clear majority.

Tunisia's Administrative Court rejected appeals filed by Marzouki against the results and the election commission announced a run-off vote would be held in December.

Security tight as polls open

The eve of the election was marked by violence with the shooting of a soldier near the city of Kairouan.

Extremists warned there would be further attacks on security forces in a video that appeared on social media networks last week.

The authorities said around 100,000 police officers and soldiers had been deployed to secure polling stations.

Polls are due to close at 1700 GMT and the result is expected to be announced sometime between Monday and Wednesday.

lw/pfd (AP, AFP, Reuters, dpa)