Appealing to Nigeria's youth to come out and vote, outsider candidate Peter Obi on Saturday rallied thousands of supporters in Lagos in his last stage of campaigning before this month's presidential election.

Chanting "Obi, Obi, we will follow you", crowds danced to Afrobeats stars on stage in a Lagos sports stadium, blowing plastic horns and waving flags for a candidate promising a "new Nigeria".

Obi, 61, has emerged as the first third party candidate to challenge the dominance of Nigeria's ruling All Progressives Congress (APC) party and main opposition Peoples Democratic Party (PDP) who between them have governed since the end of military rule in 1999.

Nearly 100 million will vote on February 25 in Africa's most populous nation to chose the successor to President Muhammadu Buhari, who steps down after two terms with Nigeria struggling with widespread insecurity and economic malaise.

A former southeast Anambra state governor, Obi has captured the interest of many young voters with a campaign offering hope for change from the patronage politics and old guard candidates fielded by the mainstream parties.

"When we win the election, it is the beginning of a new Nigeria," he told the Lagos crowd. "We are not going to change everything overnight... I assure you what we will do here nobody will believe it. Hold us responsible."

Some polls show Obi leading, but analysts say the wealthy businessmen faces a challenge to win over enough voters in the mostly Muslim north, a key block of ballots that helps determine Nigeria's election.

To win the presidency, candidates must garner the most ballots and also 25 percent of the votes in two thirds of the country's states.

Nigeria is almost equally split between the mostly Muslim north and a predominantly Christian south with three main ethnic groups, Yoruba, Hausa and Igbo, and hundreds of local languages across the country.

Election campaigns in the past often featured candidates appealing to their ethnic base to win over voters.

- National structure -

Critics say the Labour Party does not have the national structure and the state governors to help mobilise voters to get Obi elected across the country's geographic spread.

But after eight years under Buhari's APC party, with poverty on the rise and insecurity, mass kidnapping and criminal militia gangs rife, many Nigerians say they are looking for a change.

The race has emerged into a potential tight, three-way challenge.

"He is the only one who tells the truth. Here, we only had two parties for so many years, so now we want someone different," said David Sunday, 30, a food trader who voted twice before for PDP candidates.

"Obi is like our future and we want our country back."

With nearly 10 million new voters this election, and most under the age of 34, the youth vote is key.

Part of Obi's appeal has also tapped into youth who backed the 2020 #EndSARS protest movement against police brutality that spiralled into demands for better governance before it was violently suppressed.

"We are tired of bad governance in Nigeria," said #EndSARS activist Aisha Yesufu at the Lagos rally.

APC has fielded former Lagos governor Bola Tinubu, 70, known as the "Godfather of Lagos" for his political influence.

PDP's candidate is Atiku Abubakar, 76, a former vice president and businessman who boasts his experience to be able to "rescue" Nigeria. He is on his sixth run at the presidency.

Both tout their government experience and have brushed off past allegations of corruption.

Labour Party representative Yunusa Tanko dismissed worries about Obi's lack of northern support.

He said the party expected to win in the key south state of Rivers, and also take some of Lagos from the APC candidate Tinubu who considers it his home turf.

But the election mathematics are complicated in Nigeria, especially this year.

"For the Labour Party to defeat the ruling APC in a presidential election, it has to win the states that the PDP traditionally wins, and perform well in some of the APC's strongholds in the South-west, North-east, and North-west," SBM Intelligence analyst group said in a report.

Since the return to democracy in 1999, Nigeria's elections have also often been marred by violence, delays, logistical problems and vote buying accusations.

In 2019, the elections were delayed by a week just hours before voting began because of problems getting electoral material to polling stations.

Electoral authorities have expressed concerns insecurity, fuel shortages and even a shortfall of cash in banks may hinder organisation of the presidential ballot.