Legislative elections will be repeated across a large chunk of Haiti, where recent polling turned deadly and voter turnout reached only 18 percent.
Haiti's Provisional Electoral Council (CEP) on Thursday made the announcement at a press briefing, at which it had been expected to reveal results from the first-round election.
Instead, officials said winners' names were available on the CEP website, which went down following the announcement. They then left under police escort.
National Police forces had been mobilised amid concern that the CEP's results announcement could trigger another round of violence, and forces from the MINUSTAH mission of the United Nations were at the ready.
However, in the absence of results, no major incidents were reported in Port-au-Prince or big cities.
The CEP has vowed to take action against the perpetrators of crime and sporadic violence that killed two people and forced dozens of voting centres to close during the August 9 elections.
Electoral adviser Nehemy Joseph said political parties that contributed to the violence would be excluded from the election.
Already, a total of 16 candidates have been disqualified ahead of the October 25 second-round vote over their suspected involvement in the crime and violence.
CEP officials used the press briefing to announce that Haiti's first-round election will be redone across 25 of the country's 119 constituencies, where less than 70 percent of ballots were sent back to the vote counting centre in Port-au-Prince.
The entire Chamber of Deputies and two thirds of the Senate are up for vote in the long overdue elections, the first in Haiti since President Michel Martelly took power in 2011.
Haiti suffers from chronic instability, and continues to struggle to recover from a devastating 2010 earthquake that killed more than 250,000 people and crippled the nation's infrastructure.
Its parliament was dissolved on January 13 this year, and the legislative chambers have remained empty for months.
More than 1800 candidates from 128 registered parties were vying for 139 posts in the two houses.