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.
Russian attack on Ukraine's Odesa region killed two people, injured three
A Russian attack on Ukraine's southern Odesa region killed two people and injured three overnight, Ukraine's emergency service and a government official said on Monday.
Duterte was 'pivotal' in murder of thousands, ICC prosecutors say
Former Philippine President Rodrigo Duterte was "pivotal" in the murder of thousands of people during his rule, prosecutors at the International Criminal Court (ICC) said on Monday, as they pushed for his trial to go ahead.
Powerful winter storm shuts schools, disrupts travel across US Northeast
Children across parts of the US Northeast will stay home on Monday as a powerful winter storm forced school closures and pushed offices and transit systems onto emergency schedules, with officials across the region warning of dangerous travel conditions.
At least 19 killed in Nepal bus crash
A passenger bus plunged 200 metres (650 feet) from a mountainous road in west Nepal before dawn on Monday, killing 19 people including three foreign nationals.
Human rights are under assault, says UN Secretary General
Human rights are under assault worldwide, the United Nations chief warned on Monday, citing widespread abuses of international law and devastating civilian suffering in conflicts in Sudan, Gaza and Ukraine.
