Elections in parts of Nigeria have been extended until Sunday after delays and a number of attacks.
The delays were “not widespread” but were still “a matter of concern”, Commissioner Chris Yimoga told journalists in Abuja.
Technical problems with new biometric cards slowed down voter registration, even affecting President Goodluck Jonathan.
More than a dozen people have reportedly been killed in various attacks by unknown gunmen.
Jonathan is facing a strong challenge from Muhammadu Buhari.
The election is said to be the most closely fought since independence.
It was postponed from mid-February to allow the army to recapture territory from the Islamist militants of Boko Haram, reports the BBC.
The two 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 violent incidents at polling stations in which at least 13 were reported to have been killed.