Huge crowds came out for Haiti's first election since the ouster of former president Jean-Bertrand Aristide, swamping some polling stations and forcing authorities to extend voting hours.
Some polling stations opened hours late and scuffles broke out as poorer voters accused the country's elite of election fraud. Elsewhere, at least one man died and dozens of people were injured during crushes as voters waited in lineups that stretched for more than a kilometre.
They were under the eye of thousands of UN peacekeepers deployed to guard against intimidation and attacks from armed thugs.
Haitian officials and members of the 9,000-strong UN force hailed the election as a success, saying there hadn't been any sign of the violence that had been feared.
Although official figures may not be available until Friday, a huge proportion of the 3.5 million registered voters appeared to have turned out to choose a new president and a 129-member parliament.
"The people have voted massively," Juan Gabriel Valdes, a UN envoy, told the Associated Press.
'The rich are trying to steal the election'
Angry demonstrations broke out when some stations near the most violent neighbourhoods in Port-au-Prince remained closed for hours after they were supposed to open, at 6 a.m. EST.
At one location near the CitÃ© Soleil slum in the capital, more than 5,000 people gathered to vote but were told there were no ballots or other voting materials available. The polling station eventually opened three hours later.
Some protesters denounced the delays as part of a conspiracy to block votes from slum areas that have been the strongest sources of support for presidential frontrunner RenÃ© PrÃ©val, a former Aristide protege and champion of the poor.
They pointed out with anger that voting proceeded in the wealthier neighbourhoods that largely favour PrÃ©val's chief rival, Charles Baker, an industrialist from the country's elite.
"The rich are trying to steal the elections. We will not let them," Jean Biemaime, a young slum dweller, told Reuters news agency.
The confusion led Haiti's electoral council to extend polling hours by several hours. They blamed delays on logistical problems such as a shortage of workers, missing ballots and the sheer scale of the voter turnout.
'It's been a great day'
Despite the occasional chaos, officials said voters waited patiently and peacefully at most polling stations.
Some rose before dawn and walked for kilometres for the chance to partake in the election, which is seen as a key step in stabilizing a country on the verge of failure.
"The voters are out there. It's been a great day, the feeling is wonderful," Patrick Elie, a Haitian activist in Port-au-Prince, told CBC News.
"I stood in line for at least an hour and the people, they just were joking with each other and so determined to vote."
There were 35 candidates vying for the presidency. If no candidate wins a majority, a runoff between the top two would be held on March 19.
Aristide was ousted in 2004 and remains in exile in South Africa.
Since his departure, a wave of kidnappings and political killings has terrified the middle class and the poor alike.
The election had been postponed several times in recent months due to security and logistical concerns.