On Sunday, Nigeria released preliminary election results, but a winner in the contest to successor President Muhammadu Buhari is not expected for several days.
Although several voting places were vandalized and many others began late, the election in Africa's most populous nation was generally peaceful.
On Saturday, about 90 million people were eligible to vote for Buhari's successor, with many Nigerians expecting that a new leader would better combat insecurity, economic malaise, and rising poverty.
In Nigeria's 36 states, presidential and parliamentary election ballots are tabulated before transmission to the electoral commission's central tallying centre in Abuja.
The initial results from Ekiki state indicated that the majority of presidential votes were cast for Bola Tinubu of the ruling All Progressives Congress (APC).
Tinubu received more than 200,000 votes in the state, compared to less than half that number for Atiku Abubakar of the principal opposition Peoples Democratic Party (PDP) and just over 11,000 for Peter Obi of the Labour Party.
The chairman of Nigeria's electoral commission (INEC), Mahmood Yakubu, postponed the session after the first results were announced and announced that the announcement of totals would continue on Monday at 11 a.m. local time (10:00 GMT).
In a few areas of the country, voting had to be prolonged into Sunday due to problems on Saturday, but counting has already begun, and the final figure is likely within five days.
It was unclear whether all voting had been completed in the oil-exporting country in West Africa.
Earlier on Sunday, PDP's Abubakar urged INEC to swiftly post the results after accusing many state governors of attempting to tamper with the results.
"Subverting the will of the people as freely expressed in yesterday's elections would be a disservice to Nigerians and an affront to democracy," he added.
Abubakar claimed widespread electoral fraud after losing to Buhari in the 2019 election. The Supreme Court ultimately dismissed his appeal.
Julius Abure, chairman of the Labour Party, has also accused election authorities of failing to upload results from portions of Lagos and southern Delta State to aid the candidate of the ruling APC.
Monitoring organization Yiaga Africa expressed "deep concern" over the delay in results.
However, INEC stated that problems with uploading results to its IReV data page were due to "technical difficulties" and that tampering was not possible.
"The commission wishes to assure Nigerians that the problems are not the result of any intrusion or sabotage," it stated.
"It is crucial to avoid statements and actions that could inflame the current political climate."
Al Jazeera's Mohammed Jamjoom reported from Abuja that the delays in preliminary results posting by the electoral commission generated "considerable concern" among political parties, candidates, and voters.
Jamjoom stated that the "electoral commission is concerned based on their remark."
"They wish to reassure citizens that there has been no misconduct and that this is merely a technological error. I will say, though, that the longer people wait here, the more we hear from individuals in Abuja that they are concerned about what all this implies and how the delay could affect the country's future.
"People are tense, they want results, and they want to know who will be the next leader of this country at such a crucial time."
The commission has fourteen days to declare the results officially, but the online tally should be available in the coming days.
To win the president, a contender must win at least 25 per cent of votes in two-thirds of Nigeria's 36 states.
Some states must be won. Lagos has the most registered voters, with over 7 million, followed by two predominantly Muslim northern states, Kano and Kaduna.
Several observers predict an unprecedented runoff between the two frontrunners if no one satisfies election standards due to the tight race. It must be organized within twenty-one days.