Nigerians vote in presidential election
Tens of millions of Nigerians have taken part in Africa's biggest presidential election, amid hopes of the most credible poll in two decades.
Votes are already being counted in parts of the country, with official results expected on Monday.
Voting is reported to have generally gone smoothly, despite some reports of fraud and incidents of violence.
President Goodluck Jonathan's main challenger is Muhammadu Buhari, an ex-military leader popular in the north.
Some violence has been reported, with a woman said to have been killed in the central city of Jos and two bomb explosions in the north-eastern city of Maiduguri.
Dozens of people were killed in the run-up to the vote.
The polls closed at 1700 (1600 GMT), but anyone already in the queue by then was still being permitted to vote.
According to the law, counting should start immediately at the polling stations after everyone has voted.
Mr Jonathan has staked his reputation on the conduct of the election, repeatedly promising it will be free and fair.
He cast his ballot in his home state of Bayelsa in the oil-rich Niger Delta.
After voting, he said the election was a "new dawn in Nigeria's political evolution".
"If the ballot paper means nothing then there is no democracy… Nigeria is now experiencing true democracy where we the politicians have to go to the people," he said.
He said he was confident of victory, but that he would leave office if he lost, adding that he hoped there would not be a run-off because elections cost a "colossal sum of money".
Other challengers for the presidency include former anti-corruption chief Nuhu Ribadu and Kano state governor Ibrahim Shekarau, though both are seen as rank outsiders.
In Daura, home to Gen Buhari, crowds waited for hours despite the intense heat to cast their votes.
"There's a desperate attempt by the ruling party to rig this election in a more sophisticated way," Gen Buhari told the BBC.
"This time around - the level of awareness and commitment by the masses is what has given me some relief."
Gen Buhari added that he had more faith in the Independent National Electoral Commission (Inec) this time round, adding that "probably 60% of the election will be credible".
Africa's largest oil producer has long been plagued by corruption and has a history of vote fraud and violence.
Reports from Jos say a woman was killed in an argument between voters and election officials.
In other unrest
- An explosion tore through the Maiduguri election commission office on Friday night, and there was another blast at a police station early on Saturday
- An Inec office in Misau, in the north-eastern state of Bauchi, was set on fire when voters found that not enough ballot papers had been sent to the area, and were not satisfied with the explanation from the Inec official
- In Dutse, a town in the north-western state of Jigawa, a Nigerian election observer was reportedly beaten up by security staff of state governor Sule Lamido after witnessing ballot-stuffing
Voters expressed hope that the election would be fairer than previous votes.
Williams Beacher, a voter in Kano, said he had confidence in the new election chiefs.
"In previous elections, before we finish casting our vote, the national result had already been announced," he said.
Allegations of ballot-stuffing plagued the 2007 election, which brought Mr Jonathan to power as the vice-president.
He took over as president in 2010 when the incumbent died, becoming the first leader from the oil-producing Niger Delta region.
Mr Jonathan's People's Democratic Party lost seats in a parliamentary election last week.
But he remains favourite in opinion polls, and his chances have been boosted after Mr Buhari and Mr Ribadu failed to agree a formal alliance to run against him.
The relatively successful conduct of the parliamentary election has increased confidence in the ability of the electoral commission, Inec, to ensure a fair presidential vote.
With 74 million registered voters, Nigeria has the biggest electorate on the continent.
To win at the first round, a candidate not only needs the majority of votes cast, but at least 25% of the vote in two-thirds of Nigeria's 36 states. Goodluck Jonathan, of the PDP, reached that threshold in 31 states; runner-up Muhammadu Buhari of the CPC only did so in 16 states.
Nigeria's 160 million people are divided between numerous ethno-linguistic groups and also along religious lines. Broadly, the Hausa-Fulani people based in the north are mostly Muslims. The Yorubas of the south-west are divided between Muslims and Christians, while the Igbos of the south-east and neighbouring groups are mostly Christian or animist. The Middle Belt is home to hundreds of groups with different beliefs, and around Jos there are frequent clashes between Hausa-speaking Muslims and Christian members of the Berom community.
Despite its vast resources, Nigeria ranks among the most unequal countries in the world, according to the UN. The poverty in the north is in stark contrast to the more developed southern states. While in the oil-rich south-east, the residents of Delta and Akwa Ibom complain that all the wealth they generate flows up the pipeline to Abuja and Lagos.
Southern residents tend to have better access to healthcare, as reflected by the greater uptake of vaccines for polio, tuberculosis, tetanus and diphtheria. Some northern groups have in the past boycotted immunisation programmes, saying they are a Western plot to make Muslim women infertile. This led to a recurrence of polio, but the vaccinations have now resumed.
Female literacy is seen as the key to raising living standards for the next generation. For example, a newborn child is far likelier to survive if its mother is well-educated. In Nigeria we see a stark contrast between the mainly Muslim north and the Christian and animist south. In some northern states less than 5% of women can read and write, whereas in some Igbo areas more than 90% are literate.
Nigeria is Africa's biggest oil producer and among the biggest in the world but most of its people subsist on less than $2 a day. The oil is produced in the south-east and some militant groups there want to keep a greater share of the wealth which comes from under their feet. Attacks by militants on oil installations led to a sharp fall in Nigeria's output during the last decade. But in 2010, a government amnesty led thousands of fighters to lay down their weapons.