Voter regististration is delayed after electoral workers ask to be paid in advance.
Previous elections have been tarnished with fraud claims and organisational problems since Mathieu Kerekou, a military ruler and former Marxist, introduced multi-party democracy in 1991.
A shooting attack on Yayi’s convoy as he returned from an election campaign rally in the north of the country raised questions over the president’s security.
Yayi said the attack was an assassination attempt by those opposed to his anti-corruption campaign.
A former head of the West African Development Bank whose election ended more than three decades of rule by a political clique, Yayi has made fighting corruption a cornerstone of his plan to revive Benin‘s cotton-based economy.