As the counting got under way in some centres late on Tuesday, voters elsewhere still waited their turn to cast ballots at the small cardboard voting booths. Results were not expected before Friday.
International observers hailed Haitians' determination to participate in the election for a successor to Jean Bertrand Aristide, the last elected president, who fled the turmoil-torn country two years ago.
Throngs of people walked for hours in the absence of public transportation to voting centres, only to find massive lines outside.
Hour-long delays in opening many voting stations stirred widespread anger, after vote officials failed to show up on time.
A policeman and a civilian died of gunshot wounds and four others were injured when a crowd rushed the gates of a voting centre in the northwestern town of Gros Mornes, a local radio station reported.
In Port-au-Prince, one man was asphyxiated, another died of a heart attack and several more were wounded during similar stampedes, officials said.
A Chilean peacekeeper was
stabbed during the voting
More people were reported wounded in other parts of the country, including a Chilean peacekeeper who was stabbed as he intervened in a fight outside a voting centre.
Officials of the 9500-strong UN military and police force in Haiti, said 22 people were wounded, four of them seriously, when the wall of a voting centre collapsed in St Louis du Nord.
The situation calmed down later in the day.
Electoral authorities ordered voting offices to remain open as long as people were still in line. The message did not reach all the centres in time, meaning some still closed at 4pm (2100 GMT) as initially scheduled.
At a school in the Bel Air shantytown near the presidential palace, about 16 people counted ballots by candlelight as an observer from the US embassy watched on.
Despite problems during the elections, which had been postponed four times since November, international observers hailed the very fact that the voting could be held in a country terrorised by armed gangs, plagued by rampant poverty, and with a history of fraudulent elections and military coups.
UN forces kept a close watch on the election.
Armoured personnel carriers were positioned in key areas of the capital, particularly near the notoriously violent Cite Soleil slum.
Thousands of people staged a protest march, decrying the delays and the fact that residents of Cite Soleil were forced to cast ballots in neighbouring areas due to security concerns.
In the dirt-poor slums of the capital that have been hotbeds of violence, many back Rene Preval, the former president and a former ally of Aristide.
Wishick Dagrin, 45, an office employee who stood in a long line outside a voting centre for Cite Soleil, said: "All here are voting for the same candidate."
Aristide, Haiti's former president,
fled the country in 2004
Dozens of others immediately cheered, chanting "Preval, Preval".
Better-off Haitians seem to have little sympathy for Preval, and generally favour Charles Henry Baker, 50, or Leslie Manigat, 75, another former president.
Alex Turner, 53, a businessman, said: "We should not be afraid of change, we should not return to the old ideas."
Opinion polls ahead of the election gave Preval a lead of at least 27% over Baker and Manigat.
Should no candidate obtain 50% of the vote, the front runner would face off in March with his closest rival.
Officials said it could take about three days to compile the results.