A group of Haitian presidential candidates -- including all but one of the frontrunners -- alleged that the country's election is rife with fraud and called for their supporters to take to the streets in protest, hours after polls opened across the Caribbean nation.

During a hastily arranged press conference Sunday afternoon, 12 of the 19 presidential candidates made a joint announcement to that effect. They want Haitians to direct their anger towards the country's Provisional Electoral Council, known locally as the CEP, by holding public demonstrations.

They claim that the election committee is working with outgoing President Rene Preval's Unity party to ensure that his chosen candidate, Jude Celestin, wins the vote.

"It is clear that Preval and the CEP were not prepared for elections," said presidential candidate Anne Marie Josette Bijou, who read the joint statement to a cheering crowd.

The recovery from January's devastating earthquake has been slow and whoever wins Haiti's top job will be tasked with the crucial job of overseeing how billions of dollars in foreign aid is spent.

He or she will also be faced with a growing cholera epidemic, which has killed 1,600 people, as well as a people exhausted by grinding poverty, government corruption and a spate of natural disasters.

Ninety-six candidates are also vying for 11 seats in the Senate, while more than 800 candidates are battling it out for the 99 seats in the lower house.

But it is the contentious presidential contest that has garnered all the headlines.

A number of difficulties with the electoral process have surfaced as the country moves to select its next leader, raising questions about whether the vote will be considered credible.

"Preval did this on purpose," Port-au-Prince resident Fanes Francky told the Associated Press, after he was turned away from his voting station.

Election observers from the OAS fanned out to about 40 per cent of the country's 1,500 polling stations, in addition to observers from the European Union, the United Nations and various countries, including the United States.

Canadian election observer Benoit Charette said he and his colleagues had seen "different problems" throughout the day. In some cases, he said fellow observers were barred from accessing voting stations.

Electoral officials said that a turnout of less than 40 per cent may not be considered credible.

There were also unconfirmed reports of electoral fraud.

"As soon as anybody turns their heads, it seems there's been a lot of ballot-box stuffing," Nicole Phillips, an attorney with the Institute for Justice and Democracy in Haiti, said from Port-au-Prince.

"Based on everything that we're hearing on the ground, I can't imagine that the government can credibly say these were fair elections," she added.

Such reports sparked large street demonstrations in the capital. Haitian-American musician and disqualified presidential candidate Wyclef Jean was among the protesters.

"There's a lot of frustration" and the possibility of violence, he said. "But at the end of the day, you have to either stand for something or stand for nothing."

Celestin, who is considered a leading candidate from Preval's Unity party, had a well-funded campaign but is not well known to Haitian voters. Celestin is the head of a state-run construction company whose trucks carried many of the victims of the Jan. 12 earthquake to mass graves.

His campaign sent out a text message to Haitian voters Saturday with the candidate's main message: "Let's assure stability."

But Celestin faces formidable foes in 70-year-old former first lady Mirlande Manigat and popular musician Michel "Sweet Micky" Martelly.

With the irreverent campaign slogan, "Vote for the bald head," Martelly roused young voters. But his campaign was marred by violence Friday night when shots rang out near the end of a rally. One person was killed and several others wounded in what his campaign claimed was an assassination attempt.

The question of voter turnout remained unclear, after supporters of former president Jean-Bertrand Aristide threatened a boycott when his Fanmi Lavalas party was barred from the election over an unclear technicality.

Fourteen other parties have been banned from participating in the elections, Phillips said.

In addition, hundreds of thousands of voters lost their identification cards in the earthquake and could not register to vote without them. Long lineups outside the national identification centre late last week left thousands unable to obtain a card and unsure if they would be allowed to cast their ballots.

While many of the earthquake's survivors are desperately trying to ensure they can vote, election officials were forced to admit that thousands of Haiti's 4.7 million registered voters are people who died in the January quake.

Albert Ramdin, assistant secretary-general of the Organization of American States, said the organization helped deliver 800,000 voter cards over the past few days.

"We're looking at the best elections possible under the circumstances," Ramdin told The Associated Press. "We know that the (voter) list is not complete. We know that the list is inflated. We know that much more needed to be done to be on time in terms of training of polling station workers."

Preliminary results are not expected until December 7 and a close vote could lead to a run-off.

With a report from CTV's Lisa LaFlamme and files from The Associated Press