Certain polling stations opened in the capital Porto Novo and the southern city of Pobe, witnesses said, while other stations were yet to open, including in the economic capital Cotonou.

"Some stations are open while others remain closed," witness Ibrahim Soumanou said by phone from Porto Novo.

President Boni Yayi will be seeking a second term in the ballot after he defied calls for a third postponement of the election to allow voter registration to continue.

His main challenger is Adrien Houngbedji, who is backed by many of the traditional political elites in the small West African nation.

A third major candidate, Abdoulaye Bio Tchane, could help force a run-off.