Nigeria's President Muhammadu Buhari and his closest rival Atiku Abubakar made their final appeal for votes on the last day of campaigning on Thursday ahead of a tight contest in a presidential election on Saturday that was delayed by a week.

The Independent National Electoral Commission (INEC) announced the delay in the early hours of last Saturday citing logistical reasons, just as some of Nigeria's 84-million registered voters were preparing to head to the polls.

The stakes are high as Buhari, who took office in 2015 and is seeking a second term, is locked in a race against businessman and former vice president Atiku Abubakar to lead a country that is Africa's top oil producer.

The election has largely been fought on how to jump-start growth in the country with Africa's largest economy which has seen low growth since emerging in 2017 from its first recession in 25 years. Security, amid an increase in Islamist attacks in the northeast, and corruption have also been campaign issues.

So far, there are no further public rallies planned by either man, with the unexpected extra week of campaigning stretching resources and stamina. They made their pitches for votes in a statement and via social media.

Buhari, who is campaigning on an anti-corruption platform, touted his economic record in a statement issued by his spokesperson Femi Adesina.

Nigeria's 2.4 percent growth in the fourth quarter of 2018 gave "lots of cause to cheer", the statement said.

Gross domestic product grew by 1.93 percent last year, up from 0.82 percent in 2017.

"Those who do not see any good in something not initiated by them toil endlessly to hoodwink Nigerians into believing that nothing good is happening on the economic front," the statement said.

Buhari's economic reforms are focused on infrastructure development and extending a social welfare programme to create jobs and lift the poorest Nigerians out of poverty.

Atiku, candidate of the main opposition People's Democratic Party (PDP), urged voters to remove Buhari from office in a video on his Twitter feed.

"If you do not vote you will be accepting that the next four years will be like the last," said Atiku, who has criticised Buhari's handling of the economy.

Atiku has promised to create jobs, privatise the state oil company and double the size of the economy to $900-billion by 2025, in large part by handing a larger role to the private sector.

Buhari became the first opposition candidate to unseat a Nigerian president at the ballot box.

Atiku, who backed Buhari's last election bid but left the president's ruling party in late 2017, asked his supporters to replicate Buhari's unprecedented 2015 election victory.

"This Saturday we will have the opportunity to do so again," Atiku said.