Port-au-Prince, Haiti (CNN) -- Two-thirds of the candidates in Haiti's presidential race, including one of the front-runners, denounced Sunday's national elections and called for a complete annulment of the vote due to irregularities and ballot-box stuffing.
"I am asking my country's citizens, I am asking the Conseil Electoral Provisor, the government, and I'm telling the international community that as the leading candidate I'm asking for the formal cancellation of the elections," lead candidate Mirlande Manigat told CNN.
Her campaign manager, Wimine St. Pierre, said that Manigat "is asking to void the election across the entire territory of the country because of irregularities and the ballot boxes were already stuffed with votes for Jude Celestin," the hand-picked candidate of outgoing President Rene Preval.
Manigat, along with 11 other of the 18 presidential candidates, gathered at a hotel in Port-au-Prince for what contender Michel Martelly said was an event "to denounce today's massive fraud all over the country."
In a joint communique, the candidates called for the elections to be annulled, raising a serious challenge to the credibility of Haiti's vote.
And they made an appeal to the Haitian people that could lead to trouble in the hours and days to come.
"We ask the people to mobilize right now to show their opposition to the election," candidate Josette Bijoux said to the raucous crowd.
"We need a new Haiti without fraud," he added.
Before taking the stage to issue the communique with his fellow presidential contenders, candidate Leslie Voltaire told CNN that the election was "just like the cholera," referring to the epidemic spreading across the country.
Meanwhile, the U.S. embassy in Haiti urged people to stay calm.
"We join partners throughout the international community, and call on all Haitians to remain calm. And urge all political parties to ensure that their supporters conduct themselves peacefully," said U.S. embassy spokesman Jon Piechowski. "We are following events very closely."
Polls closed Sunday evening as voters struggling to overcome January's massive earthquake and a spreading cholera epidemic cast their ballots for president and other lawmakers.
Earlier in the day, Haitians lined up at polling centers inside temporary shelters that are being used as classrooms 10 months after January's 7.0-magnitude earthquake destroyed many of the city's schools.
Voters had three ballots to fill out: a green one for president, and blue and brown ballots to elect lawmakers to the Senate and parliament. At three polling stations in the capital, CNN journalists witnessed large numbers of voters complaining that they were unable to vote because their names were missing from voter rolls.
"I voted here in 2006. My name is not on the voter list. I can't vote now. This has been done intentionally by the electoral board," one person, Delcius Jean, told CNN.
Lamise Elmidor, the supervisor at one of the station's, said Haiti's main electoral body, the Conseil Electoral Provisoir, changed the rules in this year's election. Unlike past years, voters cannot cast their ballots if their names are not found on the voting lists.
Meanwhile, the rubble-strewn streets of the capital, Port-au-Prince, were eerily quiet as Haitian authorities imposed strict measures to ensure security after past votes were plagued with violence and allegations of fraud.
Only drivers with special passes from the CEP were allowed to operate cars or motorcycles Sunday anywhere on Haiti's roadways, according to CEP spokesman Richardson Dumel.
Businesses are also banned from selling alcohol, he said, and gun licenses have been temporarily suspended until Monday.
Haiti, which has endured near constant health and environmental crises, is facing a growing cholera epidemic affecting nearly 70,000 people that many feared could further scare voters from the polls.
Tensions rose ahead of the elections in which 18 candidates are running for the post of president. Seats are also up for grabs in the Senate and in the lower house of parliament.
Nearly all of the candidates have campaigned on similar platforms -- fighting corruption, creating jobs, and addressing a series of natural disasters that has left the Caribbean nation reeling and prompted many to urge for a postponement of Sunday's vote.
According to electoral law, a candidate must win 50 percent of the vote or else the election goes to a second-round runoff -- a possibility in such a crowded field of contenders.
Among the candidates is Michel Martelly, perhaps Haiti's most flamboyant politician. Martelly's penchant for dressing in drag and organizing raucous street parties in the Haitian capital has made him a popular choice among portions of the electorate.
"Yes, I've been the bad boy," Martelly told CNN last week. "But the people of Haiti believe in that rebel status that I'm selling" which he said gives him an image of being "strong" and "courageous."
His style clashes sharply with that of the more soft-spoken Manigat, a former first lady.
The 70-year-old conservatively-dressed Sorbonne Ph.D stands to be Haiti's first female president. Her husband, Leslie Manigat, was elected president in 1988 under the Assembly of Progressive National Democrats (RDNP) party, but managed to hold onto the office only four months following his election.
"It was a coup d'etat," Manigat told CNN last week. "A military coup against him. And we had to go again in exile for two years," she said.
Leslie Manigat ran again in 2006, losing to Preval in a controversial election in which Preval failed to secure more than 50 percent of the vote, but managed to avoid a mandatory runoff.
Meanwhile, the runup to the vote has included violence.
A clash between rival campaigns Friday night prompted the United Nations to send in police to Les Cayes in southern Haiti to monitor election activity.
Last Monday, clashes erupted between supporters of two rival candidates in another southern town, resulting in at least two deaths.
And earlier this month, angry crowds in the Haitian capital tore down posters of Preval's hand-picked candidate, Jude Celestin, amid frustrations with the country's corrupt and often ineffective leadership.
Celestin, whose well-funded campaign has occasionally featured airplanes dropping confetti, currently leads the largest bloc of politicians competing for seats in both houses of the Haitian parliament.
"Tempers are flaring, there is some political discontent," said Bernice Roberts, senior Haiti analyst with the International Crisis Group. "There is a perpetual crisis of confidence among political actors. Plus there's a high level of social frustration regarding the response to the earthquake, regarding the response to cholera."
According to Haiti's Ministry of Public Health, more than 1,600 people have died as a result of the cholera epidemic that was first discovered on the island last month. More than 60,000 people have been treated for the deadly bacteria.
"All of these kind of things adds up to the pressure that we have," said Max Beauvoir, Haiti's "Supreme Servitor," or highest-ranking voodoo priest. "To the point where for a problem, we don't waste time to wonder is this the cholera that got this one here, or was it the politics or was it the earthquake? It's all one. It's a vital disaster."
Beauvoir, meanwhile, said he's "praying for peace on election day."
CNN's Ivan Watson contributed to this report.