Many hope the next leader will steer Africa's most populous nation and biggest economy on a new course after years of worsening violence and hardship.
Nigerians vote for a successor to President Muhammadu Buhari in a tightly fought race dominated by three political veterans.
Nearly 90 million people are eligible to vote in Saturday's poll, which is unfolding as Africa's most populous democracy grapples with a security crisis, a sluggish economy and widening poverty.
For the first time in Nigeria's modern history, a third candidate has emerged to challenge the ruling All Progressives Congress (APC) and main opposition Peoples Democratic Party (PDP).
With Buhari stepping down after two terms in office, the APC's Bola Tinubu, 70, a former Lagos governor and political kingmaker, says "It's my turn" for the presidency.
He faces a familiar rival _ PDP candidate and former vice president Atiku Abubakar, 76, who is on his sixth bid for the top job.
But the emergence of a surprise third candidate appealing to young voters, Labour Party's Peter Obi, 61, has thrown the race open for the first time since the end of military rule in 1999.
Nearly 10 million new voters registered this year, most of them under 34, representing an important bloc if they come out to vote.
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"It is not as easy to predict as before," said Kano State College public affairs lecturer Kabiru Sufi.
"It's difficult for us to make an easy prediction as to what is going to be the likely outcome."
Cash and fuel shortages in the days before the election have also left many Nigerians angry and struggling more than usual in a country already hit by more than 20 percent inflation.
Voters will also cast their ballot for Nigeria's two houses of parliament, the National Assembly and Senate.
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To win the presidency, a candidate must get the most votes, but also win 25 percent in two-thirds of Nigeria's 36 states.
If no candidate wins, a runoff will take place between the two frontrunners, an unprecedented outcome that some analysts say is a possibility this time around.
The rules reflect a country almost equally split between the mostly Muslim north and predominantly Christian south, and with three main ethnic groups across regions: Yoruba in southwest, Hausa/Fulani in the north and Igbo in the southeast.
The presidential elections have in the past often been marked by violence, ethnic tensions, vote-buying and clashes between supporters of rival parties.
Around 400,000 police and troops will be deployed around the country to protect the vote.
But security challenges are vast.
Extremists operate mostly in the northeast, bandit militias control rural communities in the northwest, and separatist gunmen have targeted INEC offices and police in the southeast.
Polling stations open at 0730 GMT and close at 1330 GMT.
INEC has given no timeline for results, but votes are expected to be tallied within a few days. Under a 2022 law, the official results have to be confirmed within 14 days of the ballot.
If a runoff is declared, the vote has to take place within 21 days.
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