By Claire Marshall
BBC News, Port-au-Prince
In the pre-dawn gloom, queues of people at a polling station in an upmarket district of Port-au-Prince stretched off in to the distance.
Voters queued from the early morning in the Haitian capital
As the sun rose, the length of the lines of people waiting became clearer.
Tens of thousands of people had arrived well before the voting stations opened to submit their choice for president.
There has been a huge turnout in Haiti's first elections since the last president, Jean Bertrand Aristide, was ousted in an armed uprising in 2004.
Auxilien Jean Dieudonna, waiting patiently with some of his friends, lives in a remote rural area way up in the mountains. He had left his house at midnight, and had walked for four hours to come and stand in line.
I asked him if it was worth it.
He smiled and enthusiastically replied, "Yes - I came to vote for my charismatic leader so he can run my country."
Like the vast majority, he plans to vote for Rene Preval.
Mr Preval, a former president and one-time ally of the exiled Mr Aristide, has dominated these elections from the start of campaigning.
Haiti's desperately poor majority believe that he is the only candidate who understands and identifies with their misery.
However, across the city, there were very different scenes.
At two separate voting stations close to the most violent areas of the capital, there was chaos as they failed to open on time.
More than three hours later, seething crowds, clutching their newly-issued voter identification cards, shouted at harassed election officials that they should be allowed to vote.
The staff, clearly overwhelmed, shuffled official papers in a panic, trying to bring some sort of order.
In the stuffy heat, empty ballot boxes left sitting on chairs were pushed and shoved by the mass of people.
Presidential candidate Rene Preval is popular among Haiti's poor
Rene Lucas, from the impoverished slum of City Soleil, said, "If we are not able to vote today we will be in a state of crisis for the next five years."
Amid the chaos, votes did eventually start being very slowly processed. However, outside on the street, several hundred started a demonstration.
Waving palm fronds, they shouted as they ran, "Mobilise, mobilise - Preval for president."
Many cried out that they were being swindled - that Rene Preval was being cheated out of victory in favour of the candidate of the rich, Charles Henry Baker.
There have been further reports of crushing and stampedes at voting stations.
So far, a heavy troop presence has stopped any serious outbreaks of violence.
It is clear though that the longer the delays go on, the greater the chance that Haiti's election day will slide in to mayhem.