Africa's most populous country goes to the polls on February 25 but has been plunged into crisis in the run-up to the vote with dire shortages of cash and fuel.

The African Union Election Observation Mission (AUEOM) is being headed by former Kenyan President Uhuru Kenyatta, who helped broker a deal to end two years of war in northern Ethiopia and is mediating in the conflict in the eastern Democratic Republic of Congo.

The AU said the objectives of the mission were to provide an "accurate and impartial assessment" of the electoral process, offer recommendations for any improvement in future polls, and demonstrate AU support "towards consolidation of democracy, peace, stability and development in Nigeria".

Nearly 100 million people will vote to choose the successor to President Muhammadu Buhari, who steps down after two terms as Nigeria struggles with widespread insecurity and economic malaise.

Meanwhile, Nigeria's electoral commission head said on Monday that 240 polling centres will not be used in upcoming elections, as no one had chosen them due to insecurity in the surrounding areas.

Separatist and gang violence is a major concern for Nigerians when they vote on February 25 for new members of parliament and for a successor to President Muhammadu Buhari.

When new voters register in Nigeria, they are allowed to choose a polling centre.

Most people choose the nearest to where they live because movement is restricted by security agencies on election day.