Furious supporters of eliminated candidates set fires and put up barricades in the streets of Haiti's capital after officials announced that government protege Jude Celestin and former first lady Mirlande Manigat would advance to a second round run-off in presidential elections.
The results were immediately questioned at home and abroad, threatening more unrest for a country wracked by a cholera epidemic and still recovering from a devastating earthquake.
Popular carnival singer Michel "Sweet Micky" Martelly trailed Mr Celestin by about 6,800 votes - less than 1%, according to the results released by Haiti's Provisional Electoral Council.
Martelly supporters set up flaming barricades near the Petionville restaurant where the tallies were announced and threw rocks at people passing nearby. Gunshots rang out and a journalist was robbed.
"If they don't give us Martelly and Manigat (in the second round), Haiti will be on fire," said a protester, Erick Jean. "We're still living under tents and Celestin wastes money on election posters."
Radio Kiskeya reported protests outside Port-au-Prince in the Haitian cities of Cap-Haitien and Les Cayes.
Much of the concern centred around conflicts between the announced results and those reported recently by a local election monitoring group financed by the European Union - the National Observation Council - which said that Mr Celestin, who is backed by outgoing President Rene Preval, would be eliminated.
"The Government of the US is concerned by the Provisional Electoral Council's announcement of preliminary results ... that are inconsistent with the published results of the National Election Observation Council," as well as US observers and vote counts monitored by domestic and international observers, the US Embassy said.
The November 28 election was plagued by allegations of fraud. Thousands of voters were disenfranchised by confusion on the rolls and there were many reported incidents of ballot-stuffing, violence and intimidation confirmed by international observers.
Officials acknowledged the rolls were both "bloated" and "incomplete", with hundreds of thousands of earthquake dead still registered and many living voters waiting for ID cards. In the last days of counting, tabulators had to sort out clearly fraudulent tally sheets.
UN Secretary-General Ban Ki-moon said the problems were worse than originally reported. But the UN peacekeepers and the joint Organisation of American States-Caribbean Community observer mission said the problems did not invalidate the vote.
The head of the OAS-Caricom mission, Colin Granderson, said before the results were announced that officials could consider putting a third candidate in the run-off if the vote is nearly tied.
An appeals period runs until Friday, with final results expected to be announced around December 20. The run-off is scheduled for January 16.
Merchants and residents had braced for rioting by supporters of the losing candidates before the results were announced, covering market stalls and jamming streets to rush home.
The protests began as soon as news of the results hit the streets. Orange fires burned on the hills above the capital, white smoke rising into the dim electric light. Rocks were thrown at the few passing cars and guns were fired in the air. The shouts of people - drunken, revelling, angry and scared - rang across barricaded streets.
Ms Manigat, a 70-year-old law professor, is the wife of former Haitian president Leslie Manigat who served briefly in the late 1980s after a much-criticised election before being deposed by a coup.
Her supporters include a powerful senator who organised violent protests in his home region ahead of the first round of voting.
Mr Celestin, a virtual unknown before the election, is the candidate of Mr Preval's Unity party. He is the head of the state-run construction company whose trucks carted bodies and rubble out of the city after the January 12 quake.
His campaign was the best-funded of the group but Mr Preval's inability to jump-start a moribund economy or push forward reconstruction after the massive earthquake drained his support.
Many voters said they would accept "anyone but Celestin", whom they equate with the unpopular Mr Preval.
Twelve of the 19 candidates on the ballot joined up on November 28 to allege that fraud was used to ensure a Celestin victory and called for the cancellation of the vote.
Ms Manigat and Mr Martelly were among them but later reversed position when officials remarked they had a chance to win.
Mr Martelly, a popular carnival singer, was a dark horse who gained widespread credibility in the days before the vote. Thousands of his supporters took to the streets of Port-au-Prince and Cap-Haitien while polls were still open, many believing he had won the race.
The much-anticipated results were released by council president Gaillot Dorsainvil and the clear winner in the bid for senate seats was Mr Preval's Unity party, which advanced to a run-off in nine races and won a 10th. An independent candidate won the 11th.
Turnout in the November 28 election was low - just over a million people cast accepted ballots out of 4.7 million registered voters.