Tunisians are voting in presidential elections, the country's first poll since the overthrow of longtime dictator Zine El Abidine Ben Ali in the 2011 uprising.
A record 27 contenders are in the race.
The frontrunners are the incumbent President Moncef Marzouki, former prime minister Beji Caid Essibsi and veteran leftist Hamma El Hammami.
Thousands of members of the security forces have been deployed to secure the polls against potential attacks by Islamist insurgents.
If no presidential candidate obtains an outright majority, a run-off vote between the top two contenders will be held on December 28.
Last month, Tunisia held parliamentary elections, in which Essibsi's secularist Nidaa Tounes party took the lead.
Both the legislative and presidential polls complete the democratisation process in Tunisia, the birthplace of the 2011 Arab Spring uprisings.
