Voting is expected to end later this evening in some parts of Nigeria, where voters were granted special dispensation after the electronic card readers developed some difficulties.
Results from the elections are not expected until Monday from the One Hundred and Fifty thousand polling stations across the oil country.
International observers have hailed Nigeria's elections, despite technical hitches, protests and reports of violence.
UN Secretary-General Ban Ki-moon said in a statement voting had been "largely peaceful and orderly".
Voting continued for a second day in some parts of Nigeria after problems with new electronic card readers.
It is expected to be a closely fought battle between President Goodluck Jonathan and Muhammadu Buhari.
Thousands of opposition supporters in Rivers State have protested against alleged killings of campaigners and voting irregularities.
Nigeria's election commission said its office there had been set on fire and it was investigating the complaints.
Mr Ban praised the "determination and resilience" of Nigerian voters, despite reports of attacks by Boko Haram militants and others.
He urged voters to maintain a "peaceful atmosphere and to exercise patience" throughout the process.
His comments were echoed by John Kufuor, the head of the regional bloc Ecowas, who said the process has been "quite peaceful, orderly and credible".
Mr Jonathan and at least three governors from his ruling party were among those whose biometric details could not be checked by the electronic card readers - new technology intended to reduce fraud.
Instead, they had to be processed by hand. Mr Jonathan's Peoples Democratic Party (PDP) called it a "huge national embarrassment" and a "vindication" of its position against the technology.
"There should have been a test-run for a smaller election before deploying it for an election of this magnitude," said Mr Jonathan's presidential campaign spokesman Femi Fani-Kayode.
About 300 polling units out of 150,000 were affected, a spokesman for the Independent National Electoral Commission (Inec) said.
The vote had been delayed by six weeks because of the insurgency by militants from the Islamist group, Boko Haram.
Both the main candidates had pledged to prevent violence during and in the aftermath of the elections.
But several hours after voting started, reports came in of attacks at polling stations.
Latest Stories
-
Adamus accused of defying court-directed Interim Management Committee
1 min -
NPP running mate saga: Frontrunners will be disappointed – John Boadu
17 mins -
As power crisis worsens, calls for truce between ECG and PURC intensify
17 mins -
Unstable exchange rate affects claims payment – Ghana Insurers Association
24 mins -
Bank of Africa Ghana donates to Chief Imam, hosts Moroccan community to mark Ramadan activities
41 mins -
We’re winning 2024 polls hands down – PNC declares
44 mins -
Zen Petroleum opens 50th fuel retail station
50 mins -
Dumsor contributed to NPP’s 2016 victory – Prof Agyeman-Duah
52 mins -
Police link prominent SA businessman to rapper AKA’s murder
1 hour -
Richard Sky’s case must also be thrown out – Sam George
1 hour -
John Kumah’s one-week observance comes off today
1 hour -
WAEC opens online registration for BECE, WASSCE, and G/ABCE candidates
1 hour -
NDC’s allegations of bias against Supreme Court unwarranted, baseless – AG
1 hour -
Akufo-Addo hiding behind judiciary not to sign anti-LGBTQI+ Bill – Asiedu Nketia
2 hours -
‘There were very curious things taking place’ – Usher’s comments about living with Diddy at 14 resurface
2 hours