Haiti is set to vote in general elections, as the earthquake-hit nation continues to battle a deadly cholera epidemic.
Up to 4.7m registered voters will cast their ballots for one of 18 presidential candidates, as well as parliamentary deputies and senators.
Violence and concerns over fraud have already overshadowed the elections.
The polls are the first since a devastating earthquake struck in January, killing 230,000 people.
Some 11,000 United Nations peacekeepers are helping provide security and logistical support to the process in a country where infrastructure is poor and many earthquake victims still live in tented camps, mostly in the capital, Port-au-Prince.
President Rene Preval, who has served two terms and cannot run again, said Sunday was "an important day for the country's future", during a recorded broadcast on Saturday.
He urged voters to act with "order and discipline" so that Haiti could move forward.
Voting is due to start at 0600 local time (1100 GMT) and finish at 1600 (2100 GMT).
Among the frontrunners are Jude Celestin, an engineer backed by President Preval, Michel Martelly, a music star and Mirlande Manigat, a former first lady.
Ms Manigat, who is pushing education and pledging a break from corruption, is leading opinion polls by eight points.
Occasional violence has broken out during generally colourful and peaceful campaigns. At least one person was killed and several wounded when gunmen opened fire at a rally for Mr Martelly late Friday. Two others were shot dead earlier in the week in Beaumont, in south-western Haiti.
Some candidates, including Ms Manigat and Mr Martelly, have already said they are concerned about the possibility of vote-rigging.
Many Haitians have been standing in long queues over recent days to register for the polls.
"I hope I will get my voting card. It is my duty to vote, it is for my country after the cholera and the earthquake," Josue Phanon told AFP.
But some Haitians say they do not feel motivated to vote.
"We have nothing to eat and no place to live, we are so thin that even the air that blows can lift us, from where do we get the strength to go out and vote?" one woman, Carline Estinvile, told the BBC.
There have been some calls for the elections to be delayed due to spreading cholera, which has claimed 1,600 lives since the outbreak began in October. Thousands of others have contracted the disease.
Results are due to come in from 5 December onwards, with the final tally to be announced on 20 December.