Citizens are going to the polls today after a last-minute postponement earlier this week.
The main challenger to reigning president Muhammadu Buhari is former Vice-President Atiku Abubakar.
It is not known exactly when the final results will be announced.
Experts say a winner could be declared as late as Tuesday.
Nigeria is Africa's most populated country.

Keiko Fujimori declared winner of Peru presidential race
Ukrainian rescuers clear rubble as Kyiv mourns 30 killed in Russian attack
Monaco blast suspect is a Ukrainian woman who fled to Germany
Clinical trials begin for two potential Ebola treatments
India issues notice to Telegram, Signal on concerns over usernames, source says
