Nigeria election 2019: Atiku Abubakar challenges Muhammadu Buhari
Votes are being counted in Nigeria's closely-fought general election, with voting hours extended in some places following delays in the morning.
The main challenger to President Muhammadu Buhari, 76, is the former vice president, Atiku Abubakar, 72.
Whoever wins will have to address power shortages, corruption, security threats, and a sluggish economy.
The election had been due to take place a week ago but was delayed at the last minute for logistical reasons.
President Buhari cast his ballot in his hometown of Daura in the northern state of Katsina. Asked if he would congratulate his rival if he lost, he said: "I will congratulate myself."
Why was the election delayed?
The initial vote was rescheduled in a dramatic press conference in the early hours of Saturday 16 February, just five hours before polls were due to have opened.
The Independent National Electoral Commission (Inec) has given several reasons for the delay, including attempted sabotage and logistical issues such as bad weather and problems with delivering the ballot papers.
Inec has said that everything is in place for the poll to take place this time round.
How will the election work?
The candidate with the most votes is declared the winner in the first round, as long as that person gains at least 25% of the votes in two-thirds of Nigeria's 36 states.
There are 73 registered candidates in the presidential election, but campaigning has been dominated by the two political giants and the established party machines behind them.
What are the main issues?
Nigeria is Africa's largest oil producer but corruption and a failure to invest the proceeds from the industry have hampered development in the country.
It slipped into a recession in 2016 and a slow recovery has meant that not enough jobs have been created to cope with the large number of young people coming into the employment market. Currently nearly a quarter of the working age population is unemployed.
Mr Buhari has quelled a militant Islamist rebellion in the north-east of the country, but Boko Haram remains active. There has also been an upsurge in violence in the country's Middle Belt as traditional herders and more settled farmers have clashed.
Up until 1999 Nigeria was governed by either short-lived civilian administrations or military rulers. But this year marks 20 years since the return of democracy.
Mr Buhari was elected in 2015 – the first time an opposition candidate had defeated an incumbent to become president.