All Progressives Congress (APC) party officials Festus Keyamo, left, Femi Fani-Kayode, center left, and Dele Alake, center right, speak after a press conference underneath a photograph of presidential candidate Bola Tinubu in Abuja, Nigeria Monday, Feb. 27, 2023. AP
"The election is irretrievably compromised and we have totally lost faith in the entire process," Labour Party chairman Julius Abure told reporters along with representatives of the Peoples Democratic Party (PDP).
"We demand that this sham of an election should be immediately cancelled," Abure said. "We also call for a fresh election to be carried out."
Early tallies from Saturday's election show ruling All Progressives Congress (APC) party candidate Bola Tinubu ahead of PDP's Atiku Abubakar and the Labour Party's Peter Obi.
Voting was mostly peaceful, but many polling stations opened very late and delays and technical problems disrupted uploading of tallies from local polling stations to a central website.
The country's election overseer, the Independent National Electoral Commission (INEC), said problems were technical glitches.
But opposition say failures in the system allowed for manipulation and disparities in the results.
"This election is not free, and far from being fair and transparent," Abure said.
"President Muhammadu Buhari, this is the time of a great test of your integrity. Use your office to save Nigerians from this electoral mismanagement."