- By Nduka Orjinmo
- BBC News, Abuja
The results are expected in Nigeria’s first tough election since the end of military rule in 1999.
However, voting in some parts of the country has been postponed until Sunday following widespread delays and some attacks on polling stations on Saturday.
Elsewhere, polling continued through the night.
Turnout appears particularly high among young people, who make up a third of the 87 million eligible voters.
This makes it Africa’s largest democratic exercise.
The election has seen an unprecedented challenge to the two-party system that has dominated Nigeria for more than two decades.
Relatively unknown Peter Obi of the Labor Party is seen as a potential winner alongside Bola Tinubu of the ruling All Progressives Congress (APC) and Atiku Abubakar of the main opposition Peoples Democratic Party (PDP). There are 15 other presidential candidates.
Voting on Saturday was marred by long delays at polling stations, as well as widespread reports of ballot box looting and attacks by armed men.
Dr. Nkem Okolie was about to vote in the Lekki district of Lagos, the largest city, when masked men stormed the polling station.
“There was chaos. Bottles were flying everywhere,” he told the BBC. “They were broken [the ballot box]. They stole the officers’ phones. Now we can’t vote.
In at least five states, polling did not begin until around 18:00 local time in some places – three and a half hours after polling closed.
Tension prevailed in some parts of Rivers and Lagos states, where some political parties asked their members to go to polling centers to stop their manipulation.
There have also been complaints about the use of the recently introduced electronic voting system, with many voters accusing election officials of refusing to upload results at polling stations.
However, in areas where polling went smoothly, results have already been released outside individual polling stations.
These results are then aggregated from tens of thousands of polling stations across the country. An official from the electoral commission in each of Nigeria’s 36 states will travel to the capital, Abuja, where the results will be announced state by state, with the first announcements expected late Sunday.
Final results are not expected before Monday, and could be as late as Wednesday.
In a press conference on Saturday, Election Chairman Mahmoud Yakubu apologized for the delay in voting.
Mr Yakubu said armed men attacked some polling stations in the southern state of Delta and the northern state of Katsina, where voter card verification machines were taken away.
Later they were replaced and security was beefed up for polling.
Mr Yakubu said militant Islamists opened fire on election officials from a hilltop in the Kwoza area of the northeastern state of Borno, injuring several officials.
The run-up to the vote was overshadowed by a cash crunch caused by the currency overhaul, leading to widespread chaos at banks and cash machines as desperate people scrambled to access their cash.
New notes were introduced to deal with inflation and to buy votes. Ahead of the election, a member of the House of Representatives was arrested with nearly $500,000 (£419,000) in cash and a list of people he owed it to.
No matter who wins, 10,000 people were killed last year.
Voters also voted for 109 federal senators and 360 members of the House of Representatives, with another vote for state governors in March.
Who are the main candidates?
Mr Obi, 61, enjoys strong support among some sections of Nigeria’s youth, particularly in the south.
Despite being in the PDP before that, he is seen as a relatively new face. The wealthy businessman served as the governor of the south-eastern state of Anambra from 2006 to 2014. His supporters, known as “OBIDients”, say he is the only honest candidate, but his critics argue he is a waste of a vote. Both the traditional parties are likely to win.
Instead, the PDP, which ruled until 2015, wants Nigerians to vote for Mr Abubakar, 76 – the only major candidate from the country’s predominantly Muslim north.
He has run for president five times before – losing all of them. He has been dogged by allegations of corruption and cronyism, which he denies.
Most of his career was spent in the corridors of power, serving as a top civil servant, vice president and a prominent businessman.
Most people see the election as a vote on the APC, which has overseen a period of economic crisis and worsening insecurity.
Its candidate, Mr Tinubu, 70, is credited with building Nigeria’s commercial hub Lagos, where he served two terms as governor until 2007.
He is known as a political godfather in the South West region, where he wields great influence, but like Mr Abubakar, he has been dogged by allegations of corruption and ill health over the years, both of which he denies.
In Nigeria’s 36 states, a two-thirds majority of votes and 25% of the votes are required for a candidate to be declared the winner.
Otherwise, there will be a run-off within 21 days – a first in Nigeria’s history.
Additional reporting from BBC teams across the country.