Nigeria's Independent National Electoral Commission has begun announcing official results from Saturday's presidential election.
But just minutes into the national tally Monday, party agents challenged the outcomes. Last weekend's polls were marred by delays and technical problems that saw thousands of voters hit the streets Sunday in protest.
The Abuja national collation center opened at midday Monday for the second day of vote counting.
Officials from Nigeria's electoral body INEC along with election observers, party members and journalists were present.
INEC announced early results from four out of Nigeria's 36 states putting the All Progressives Congress presidential candidate, Bola Ahmed Tinubu, in the lead.
Ekiti, Osun, Ondo and Kwara states are considered strong bases for the incumbent APC party.
But the announcement of results was met with resistance from political parties. They said INEC's field officers failed to upload the latest results from polling units in order to manipulate the figures.
INEC's Mahmood Yakubu addressed the issue.
"The law does not require that collation should be done on the basis of results transmitted, it's on the basis of results carried forward manually, physically to the various collation centers, but when there are discrepancies, it is the transmitted results that should be used to dissolve the discrepancies," he said.
All three top contenders have questioned the vote counting, including Nigeria's Labor Party.
During a media briefing Sunday, the party said it will only accept results that corroborate with their agents' tallies at polling units.
The elections Saturday were marred by widespread delays, technical difficulties with the voting machines, and threats of violence and insecurity. The delays forced INEC to extend voting into a second day on Sunday.
But some eligible voters did not get a chance to cast their ballots.
On Sunday, hundreds including Abuja resident Kingsley Francis waited several hours for electoral officials to arrive.
"We had to queue, I was number one to be accredited but after the accreditation no paper was given to me. Other people were getting accreditation, no paper was given to them," he said.
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Local and international observers are also raising concerns.
"At the end of our observations, we will make recommendations on how to improve the process because elections in our region are evolving. And we must continue improving and trying to harmonize them," he said.
The race to replace outgoing President Muhammadu Buhari is expected to be highly competitive.
Candidates for the biggest parties, PDP and APC, are facing a fierce challenge from the Labor Party's Peter Obi. Obi is mostly backed by young people, who accounted for over 80 percent of the 10 million first time voters.