Lagos in play as Nigerians vote for governors
STORY: Polls opened on time at 0730 GMT in most places but election officials arrived late in some areas. Voting ends at 1330 GMT.
The Independent National Electoral Commission (INEC) is under scrutiny after observers from the European Union, the Commonwealth and other bodies reported several problems during last month's voting, among them failures in systems designed to prevent vote manipulation.
The observers criticized the INEC for poor planning and voting delays but did not allege fraud.
Governors wield enormous influence in Africa's most populous nation of more than 200 million and their support often decides who becomes president. Some governors preside over states whose annual budgets are bigger than some small African countries.