The director of Haiti's electoral register says he fears corruption in some of the polling stations could affect the outcome of the vote.
"I think there will be fraud everywhere," Augustin said, adding that it was not impossible that the vote could be "hijacked".
"We need massive participation and many observers and journalists" to ensure a fair election, he said.
Fighting to succeed President René Préval are Jude Célestin, Préval’s favourite, and Mirlande Manigat, a former first lady who is leading in opinion polls.
Singer Michel Martelly, also known as “Sweet Micky”, is also doing well in opinion polls and has a broad base of support among the urban masses of Port-au-Prince.
No candidate is expected to obtain the 50 per cent needed to win the election outright. Two frontrunners will probably make it through to a second round in January.
Recent clashes between political rivals and an outbreak of cholera have givern rise to calls to delay the election. But Haitian authorities maintain that the election will go ahead.
The growing cholera epidemic in the quake-devastated state has killed 1,415 people and is claiming more than 100 new lives every couple of days.