Bola Tinubu, chairman of All Progressive Congress, has received over 6 million votes ahead of his rivals, Atiku Abubakar of the Peoples Democratic Party, who has secured over 4 million votes, and the Labour Party's Peter Obi, who has got over 3 million votes.
As of Tuesday afternoon, results from 22 out of the 36 states across the West African nation have been counted.
Opposition parties, however, rejected the results, alleging that the electoral body breached the law on procedures for the collation, upload, and release of results.
Collation is done manually as opposed to uploading to the Independent National Electoral Commission (INEC) server from Bimodal Voter Accreditation System (BVAS) for everyone to see, said Dino Malaye, a PDP representative at the INEC National Collation Center, in Abuja.
"This is a breach of the 2023 electoral law and we reject the results released so far."
There is anxiety across the country on the credibility of the outcome of the election on Saturday after reports of violence, ballot theft, late arrival of voting materials, and failure of accreditation machines.
Thabo Mbeki, the head of International Election Observers Groups and former South African president, called for restraint.
"The time now is for restraint and continued patience as we await the final results," said Thabo, who leads the Commonwealth Observers team.
Authorities are expected to release the final results late on Tuesday.
Appeal for rectification
Meanwhile, Nigeria's former President Olusegun Obasanjo appealed for caution and for errors committed by electoral officials to be rectified. Speaking on a local broadcaster, Obasanjo said tension was building up in the country over the manual counting of votes.
He appealed to outgoing President Muhammadu Buhari to allow for all ballots that did not meet credibility and transparency standards to be canceled.
Olusegun said Muhammadu had proved beyond reasonable doubt that he would want to leave a legacy of free, fair, transparent, and credible elections but that the electoral body's decision to return to the manual transmission of results after investing in an electronic system that allowed instant transmission from polling units was unfortunate. He said the manual system could be easily manipulated and the results doctored.
Opposition calls for cancellation of Feb. 25 election
Nigeria's opposition parties on Tuesday called for Saturday's poll to be canceled and demanded a fresh election.
Addressing a news conference in the capital Abuja with a coalition of opposition parties -- Peoples Democratic Party and African Democratic Congress, Julius Abure, national chairman of Labour Party said they have lost faith in the independence of the electoral commission.
"We have totally lost faith in the electoral process. We demand that this election should be canceled. Labour Party, Peoples Democratic Party, African Democratic Congress, and all other allied parties shall no longer take part in the electoral process going on at the collation center," he said.
The opposition parties are also demanding a fresh election, Julius said.
"We took the decision because the Independent National Electoral Commission failed to adhere to the provision of the electoral law after several complaints by us," he told Anadolu.
He said the electoral commission ought to upload the votes from states rather than manual counting, insisting the "process is compromised."
Olusegun urged Muhammadu to intervene and refused attempts to make him view the complaints of the oppositions as trivial.
But Information Minister Lai Mohammed accused the ex-president of partisanship.
"Former President Obasanjo is in reality a known partisan who is bent on thwarting, by subterfuge, the choice of millions of Nigerian voters," he claimed.
Olusegun has been very critical of Muhammadu's policies.
*Hassan Isilow contributed to this report from Johannesburg, South Africa.
