Haitian law offers candidates the opportunity to challenge the results from the presidential and legislative election in electoral courts.
Businessman Jovenel Moise appealed for unity after official preliminary results showed he won Haiti's presidential election in the first round.
Provisional Electoral Council president Leopold Berlanger cautioned that the results were preliminary and final results would not be confirmed until December 29.
Three of the council's nine members refused to sign the results announced on Monday, signalling a potential conflict over the outcome.
Moise, a 48-year-old businessman who was backed by former president Michel Martelly but has never held political office, appealed to Haitians to unite behind him.
"I appeal to the country's youth, to all Haitians who live abroad, to all the country's professionals, to stand by my side to raise the country up, because Haiti is on its knees," he said, speaking at a luxury hotel minutes after the results were announced.
The election council's executive director Uder Antoine said Moise won 55.67 percent of the votes. Jude Celestin, candidate of the opposition LAPEH, was next with 19.52 percent.
Candidate Moise Jean Charles got 11.04 percent and Maryse Narcisse of the Fanmi Lavalas party 8.99 percent.
Any candidate who wins more than half of the votes cast in the first round is the victor.
Haitian law offers candidates the opportunity to challenge the results from the presidential and legislative election in electoral courts, before final results are published on December 29.
Moise reached out to his opponents in appealing for unity.
"This evening, I have a special thought for each of my competitors, for each citizen who was a candidate because they have a project for Haiti," he said.
"My brothers and sisters, it's together that we will change Haiti, it's together we must work to enable every Haitian man and woman to live better."
The nation was on edge as the results were announced, after past episodes of sometimes bloody violence in a desperately poor country marred by repeated episodes of political upheaval.
Interim leader Jocelerme Privert called for calm ahead of the result announcement.
"Resorting to acts of violence can only spoil the fruits of the beautiful day we had on November 20," Privert said at the presidential palace in Port-au-Prince, referring to the vote held earlier this month.
The election was a key step in restoring constitutional order in Haiti, where former president Martelly's mandate expired after the results of last year's first round poll were annulled amid widespread claims of fraud.
Nearly 6.2 million people were eligible to vote in the Western Hemisphere's poorest country, parts of which are still struggling to recover from a devastating hurricane.
Of the 27 candidates who ran for president, four had claimed victory in the first round before the official announcement in statements criticized by the international community.
"My compatriots, our country is living through a dramatic moment. It needs a social cooling off, it needs calm, serenity, peace and tranquility," Privert said.
"My brothers and sisters, I invite you all to use the means of recourse set forth in the electoral decree and constitutional provisions to defend your legitimate rights."
Haiti's election was originally held in October 2015, but the results were eventually scrapped amid opposition protests after an independent commission found massive fraud.
With the results annulled, Martelly, a popular singer elected in May 2011, was unable to transfer power to a successor chosen by popular vote, as required by the constitution.
The legislature chose Senate chief Privert as interim head of state -- initially with a three-month mandate -- but new polls were delayed amid civil unrest and political infighting.
The first round of the presidential election was scheduled again for October 9 this year, but was delayed after Hurricane Matthew pummeled the country a few days before.