Tunisia holds first post-revolution presidential poll
The election is described as the first genuinely free presidential poll in Tunisia's history
Tunisians are set to vote in the country's first presidential election since the 2011 "Arab Spring" that triggered uprisings across the region.
More than 25 candidates are in the race, but incumbent Moncef Marzouki and anti-Islamist leader Beji Caid Essebsi are widely seen as the favourites.
The poll forms part of political changes since the revolution that ousted leader Zine al-Abidine Ben Ali.
A parliamentary vote was held in October.
Tunisia - seen as the birthplace of the Arab Spring that saw political upheaval in several Arab countries - is considered to have had the most successful outcome, with relatively low levels of violence.
'Security threats'More than five million people are eligible to vote in Sunday's election, which will deliver the country's first directly elected leader since the removal of Mr Ben Ali.
Most polling stations open at 08:00 (07:00 GMT) and close 10 hours later.
Tunisians hope the election will strengthen post-revolutionary changes in the country
Security has been stepped up across the country ahead of the election
If no candidate wins more than 50% of the vote, a run-off round will be held on 31 December.
"We were the first to enter into this cycle of change which they have called the Arab Spring," Prime Minister Mehdi Jomaa was quoted as saying on the eve of the poll.
"We will be the first [to make the transition] but others will follow," he added.
Mr Essebsi, from the Nidaa Tounes (Tunisia's Call) party, is the favourite to win after his two-year-old party came first in the parliamentary election.
But critics say Mr Essebsi, who held positions in the governments of Mr Ben Ali and also of the first post-independence leader Habib Bourguiba, represents a return to the past.
Among the other candidates are Mr Marzouki, parliamentary speaker Mustapha Ben Jaafar, Republican Party leader Ahmed Nejib Chebbi, female magistrate Kalthoum Kannou and businessman Slim Riahi.
Tunisia is still facing the spectre of civil unrest and terrorism, with Interior Minister Lotfi Ben Jeddou warning about "serious security threats" near the Algerian border where al-Qaeda militants are said to be hiding.
The ministry says all candidates have been placed under strict security measures to ensure their safety.
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