Bola Tinubu, the candidate for the ruling party in Nigeria, is in the lead after the results from 14 of the 36 states in the nation were announced.
Just over 44% of the votes have been counted in Mr. Tinubu's favor. Atiku Abubakar, his main opponent, has nearly 33 percent of the vote.
Peter Obi of Labour has nearly 18 percent of the vote after shocking many by defeating Bola Tinubu in the biggest city, Lagos.
The parties of Mr. Abubakar and Mr. Obi left the location where the results are being announced on Monday.
The Peoples Democratic Party (PDP) and the Labour Party have argued that the new electronic voting system lacks transparency.
This was the first time an electronic device had been used to certify voters in a national election.
The opposition parties' complaints have been refuted by the Independent National Electoral Commission (Inec).
According to its chairman Mahmood Yakubu, the results announcement will continue.
The All Progressives Congress (APC), which is in power, was charged with colluding with Inec by the PDP representative at the election center in Abuja, the nation's capital. The PDP described the election as fraudulent. The Labour Party requested that the announcements be put on hold or that the election be called off and held again.
According to the APC, those who are unhappy with the outcomes should file a lawsuit and the parties should first give the procedure time to complete.
To be declared the winner, a candidate must receive the most votes nationwide and 25% of the votes cast in 25 of the 36 states plus Abuja.
The top two candidates will face off in a run-off in the event that those thresholds are not met.
Since the end of military rule in 1999, the APC and PDP have ruled Nigeria.
Mr. Obi, a candidate from the Labour Party—a previously obscure party—promised to undermine the two-party system.
Young people, who make up a third of registered voters, support him in large numbers. There are 15 additional applicants.
Mr. Abubakar received five more votes than Mr. Obi and Mr. Tinubu combined in the six states where results have been announced thus far.