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.
Second killing in Minneapolis by US federal agents sparks protests
US immigration agents shot and killed a US citizen in Minneapolis on Saturday, officials said, sparking fierce protests and condemnations from local leaders in the second such incident this month.
Massive winter storm sweeps across US
More than 400,000 customers in the US as far west as Texas were without power and more than 9,600 flights were expected to be cancelled on Sunday ahead of a monster winter storm that threatened to paralyse eastern states with heavy snowfall.
Russian strike on Ukraine's Kyiv leaves 1,700 buildings still without heat
Around 1,700 apartment buildings in the Ukrainian capital Kyiv were still without heating following a Russian missile and drone attack earlier this week, Kyiv Mayor Vitalii Klitschko said on Sunday.
Seven dead, 82 missing in Indonesian landslide
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Bombing at Pakistan wedding kills 7, police say
The death toll from a bombing at a wedding near the Afghan border rose to seven on Saturday, police said, as Pakistan struggles to deal with a rising wave of attacks.
