The tightest presidential election in Nigeria since the end of military rule in 1999 is currently in the process of being counted.
Long wait times resulted from some polling places being unable to open on time due to logistical issues and security incidents.
Many young, first-time voters arrived early to cast their ballots, indicating that turnout was high.
With 87 million people eligible to vote, the elections are the largest democratic exercise in Africa.
Since the return of multi-party democracy 24 years ago, two parties—the ruling APC and the PDP—have dominated politics.
The Labour Party's Peter Obi, who is supported by a lot of young people, is a strong challenger this time in the race to succeed President Muhammadu Buhari.
Tens of thousands of polling places are counting the results, which will then be compiled and sent to the electoral headquarters in the capital Abuja.
The final outcome won't likely be known until at least Tuesday.
Mahmood Yakubu, the head of the electoral commission, apologized for the long lines for voting but insisted that anyone in a line by 13:30 GMT (14:30 local time) would be able to cast a ballot even though polling places were supposed to close by that time.
While some voters were irate at the delays, others patiently waited to cast their ballots.
"As a Nigerian, you prepare for any situation, so I left the house with a water bottle and my power bank. First-time voter Edith told the BBC in Lagos, "I'll wait until they get here so I can cast my ballot.
In the southern state of Delta and the northern state of Katsina, Mr. Yakubu claimed that armed men had attacked some polling places and taken away voter card verification machines.
After that, they were changed out, and voting could proceed with increased security, he said.
Additionally, reports of violence and ballot boxes being stolen in Lagos, Nigeria's largest city, have surfaced.
Mr. Yakubu claimed that militant Islamists in the Borno state of northeastern Nigeria opened fire on election officials from a mountaintop in the Gwoza region, injuring a number of officials.
A cash crunch brought on by a botched currency redesign overshadowed the run-up to the election, causing widespread chaos at banks and ATMs as desperate people tried to withdraw cash.
The new notes were introduced to combat both vote-buying and inflation. A member of the House of Representatives was detained on election night with nearly $500,000 (£419,000) in cash and a list of recipients, according to the police.
Whoever prevails will have to deal with the redesign of the currency, a failing economy, high rates of youth unemployment, and pervasive insecurity that resulted in 10,000 fatalities last year.
Additionally, 109 federal senators and 360 members of the house of representatives were up for election, with a subsequent vote for state governors taking place in March.
Young people have shown tremendous interest in the election; one-third of those eligible to vote are under 35.
After joining the Labour Party in May of last year, Mr. Obi, 61, hopes to destabilize Nigeria's two-party system.
Even though he had previously been a member of the PDP, he is still viewed as a relatively new face and has ardent support from some young people in Nigeria, particularly in the south.
From 2006 to 2014, the affluent businessman presided as governor of the southeasterly Anambra State. The "OBIdients," who support him, claim he is the only candidate with integrity, but his detractors contend that casting a ballot for him is pointless because he is not likely to win.
The PDP, which ruled until 2015, prefers that Nigerians cast their votes for Mr. Abubakar, 76, the only significant candidate from the region's predominantly Muslim north.
He has previously run for president five times, losing each time. He has consistently faced allegations of cronyism and corruption, which he strongly refutes.
He has worked as a respected official, vice president, and well-known businessman, spending the majority of his career there.
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The majority of people see the election as a vote against the APC, which has presided over a time of economic hardship and escalating insecurity.
During his two terms as governor from 2003 to 2007, its candidate, Mr. Tinubu, age 70, is credited with creating Lagos, Nigeria's commercial center.
He is regarded as a political godfather in the south-west region, where he has enormous power, but like Mr. Abubakar, he has long been the target of claims of corruption and poor health, both of which he vehemently refutes.
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To be crowned the victor, a candidate must receive the most votes and 25% of the total ballots cast in at least two-thirds of Nigeria's 36 states.
If not, there will be a run-off in 21 days, which is unprecedented in Nigerian history.
* More reporting by BBC teams across the nation.
The results made public by the election commission are available here:.
