Millions of Nigerians have voted in the most credible presidential election for decades, with early results pointing to a close race between President Goodluck Jonathan and rival Muhammadu Buhari.
The polls pit front-runner Jonathan, the first head of state from the oil-producing Niger Delta, against Buhari, a northern Muslim with a reputation as a disciplinarian.
Early results showed Jonathan had done well in much of predominantly Christian southern Nigeria, including areas such as Lagos where his ruling party had struggled in a parliamentary election a week ago.
But first results from heavily Muslim northern states showed Buhari with a wide lead and a very high turnout which could help counterbalance his lack of support in the south.
To win in the first round, a candidate needs a simple majority and a quarter of the vote in two thirds of the 36 states.
There are more than 73 million registered voters and 120,000 polling stations. Final results could take days.
Election workers, party officials, observers and armed police crammed into a classroom of an Abuja school to try to collate results from 35 polling units.
Heated arguments flared and dissipated, but observers said the system was working.
Across most of the country of 150 million there was little sign of the chaos and violence that has dogged past elections although two bombs panicked voters in the troubled northeastern city of Maiduguri.
There were reports of underage voting and attempts at ballot-stuffing in some areas.
In the northern state of Bauchi youths torched an electoral commission office after officials were allegedly found thumbprinting ballot papers.
