President Buhari is stepping down after serving the maximum eight years or two terms as allowed under the country’s constitution.
About 90 million Nigerians are eligible to cast their ballots in the election in Africa’s most populous democracy that will also determine who will serve in the National Assembly.
Some 176,600 polling stations were scheduled to be open between 8:30 a.m. and 2:30 p.m. (0730 GMT to 1330 GMT).
Polling stations were scheduled to open at 8:30 a.m. (0730 GMT), though Reuters reported at several locations across the country some that were not ready. In northern Kano State, southern Bayelsa State and the federal capital Abuja, Reuters reporters saw queues of voters with no election officials in sight.
Reuters reporters at one location in central Lagos, another in the city of Awka, in southeastern Anambra State, and one in the northeastern city of Maiduguri saw voting begin, though at other Lagos locations there were delays.
Veteran candidates – Bola Tinubu, 70, a former Lagos governor from the ruling All Progressives Congress party, and former Vice President Atiku Abubakar, 76, from the main opposition People's Democratic Party – are being challenged by a third-party candidate, the Labour Party's Peter Obi, 61, who has support among young voters.
The outcome is “not as easy to predict as before,” Kano State College public affairs lecturer Kabiru Sufi, told Agence France-Press.
The election occurs as Nigeria is experiencing a cash shortage, widening poverty, high inflation and energy shortages.
In the past, Nigeria’s elections have been marred by electoral fraud and violence, but the presidential candidates promised this week to support a peaceful and transparent process.
Nigeria’s Independent National Electoral Commission has said the results of the election will be available in a few days. The commission has also introduced biometric voter IDs to help prevent fraud. The results will be transmitted electronically.
This report originated from VOA News. Some information came from Reuters and Agence France-Presse.