Polls open at 0700 GMT, with President Muhammadu Buhari, a former army general who has vowed to defeat the jihadists, seeking a second term. Nigerians began voting for a new president on 23 February after a week-long delay that has raised political tempers, sparked conspiracy claims and stoked fears of violence. Among the country's first voters, he said he was ready to congratulate himself in a race seen as too close to call.
About 120,000 polling stations opened early across Africa's most populous nation with results expected early next week. Atiku, a former vice president, has pledged to expand the role of the private sector.
The ruling party national chairman who voted at 11:45 am, however, deplored the late arrival of materials as voting started at about 10:00 am.
The Independent National Electoral Commission (INEC) last Saturday announced a one-week delay to the election, just hours before it was due to get under way.
Incumbent President Muhammadu Buhari is to face opposition presidential candidate Atiku Abubakar in the presidential election. He stressed being "very hopeful indeed" after casting his ballot.
"I am impressed by the turnout of the people", he told reporters shortly after voting.
" I have been voting since 1999".
He said the number of polling units that opened at 8am and 10am stood at 67.91 per cent, while polling units that opened after 10am stood at 16.96 per cent.
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In Twitter posts, the Nigeria Civil Society Situation Room said many polling stations are late in opening because of several problems including missing stamps, the late arrival of polling officials and faulty card readers.
That angered voters who had already travelled to their home towns and villages to participate, and saw the main parties accuse the other of conspiring with INEC to rig the result.
"After all, it is not my brother that is contesting", said Patience Okoro in Agbor in the south.
The wife of the president looks to have allowed him so to do with the entire episode drawing laughter among the people present at the booth. Delays were reported in Delta, Anambra and Akwa Ibom states as well as in Lagos, Nigeria's largest city.
An Atiku supporter in Kano, stylist Laurie Isaac, 27, said: "We need change. I need my salary to increase".
According to a report by Sahara Reporters, residents of Maiduguri, the Borno State capital, are now in panic as series of explosions have rocked the city all within ten minutes. Boko Haram had warned people not to vote.
"There have been suspicions that it was an attack by Boko Haram but we don't know yet".