Nigeria’s two major opposition parties on Tuesday called for the presidential election to be canceled and rerun, saying that it had been compromised by vote rigging and widespread violence.
The election over the weekend in the West African nation — the most populous on the continent, with 220 million people — was the most wide open in years, with a surprise third-party candidate putting up an assertive challenge.
On Tuesday, the chairmen of the two opposition parties — the People’s Democratic Party and the Labour Party — called for the head of the government’s electoral commission to resign, even as the commission continued to release results.
With about one-third of the 36 states reporting results, by Tuesday afternoon, Bola Tinubu, the candidate of the governing All Progressives Congress party appeared some distance ahead of his rivals in the count, with 44 percent of the vote. Some 87 million people were registered to vote, but results from the first tabulations suggested low turnout.
“We demand that this sham of an election be immediately canceled,” said Julius Abure, chairman of the Labour Party. “We have totally lost faith in the whole process.”
Many Nigerians had looked to the election to put the country back on track after eight years of rule by an ailing president, Muhammadu Buhari — a military dictator turned democrat. Mr. Buhari had reached his two-term limit and was not running for re-election.
Under his leadership, the Giant of Africa, as Nigeria is known, lurched from one economic shock to the next. Over 60 percent of people live in poverty, while security crises — including kidnapping, terrorism, militancy in oil-rich areas and clashes between herdsmen and farmers — have multiplied.
Shortages of fuel and cash — the latter because the government recently redesigned the currency and people could not get access to the new notes — have caused widespread suffering.
Many polls ahead of the election predicted a win for Peter Obi, the so-called “youth candidate” of the little-known Labour Party. But as of Tuesday afternoon, Mr. Obi had just 18 percent of the votes, while Atiku Abubakar of the People’s Democratic Party also trailed behind Mr. Tinubu with 33 percent.
On Monday, Mr. Obi pulled off an unexpected victory in Lagos State, home to the country’s largest city and traditionally a stronghold of Mr. Tinubu, who was its governor for eight years.
The Independent National Electoral Commission, or I.N.E.C., had said in a statement on Monday that it took “full responsibility” for the logistical problems and delays.
Dino Melaye, a spokesman for the People’s Democratic Party, said there was evidence that the All Progressives Congress party had influenced the electoral commission and that results were being changed — though he did not provide such evidence at the news conference.
His accusations were supported by Julius Abure, chairman of the Labour Party. Speaking on Tuesday on behalf of opposition parties, he said that results were “being taken to government houses for manipulation” before being released, and that election officials had not been submitting images of the result sheets from polling stations, as had been the plan.
Dele Alake, a spokesman for the All Progressives Congress presidential campaign council, rejected the idea that his party had tried to engineer a result, noting that Mr. Tinubu had lost in his home state, as other party figures had in theirs.
“How can anyone claim the election was rigged or not transparent?” he said.
Independent observers also raised concerns about whether the election was free and fair, although they stopped short of accusing the governing party and the election commission of rigging it.
A mission of European Union observers pointed to a lack of transparency and operational failures. African Union observers noted “isolated incidents of violence.”
An observer mission from the Commonwealth led by the former South African president Thabo Mbeki said the election was largely peaceful, but Mr. Mbeki also said observers had recorded “incidences of election-related violence and insecurity, some of which regrettably resulted in the loss of life and postponement of elections in some polling units.”
The number of violent incidents in the run-up to the election was double that in previous years, while there were probably at least as many episodes on the day of the election as there were in the last vote in 2019, observers from the United States said.
Voters traded their own stories of disruption, delays and irregularities.
Jude, a 32-year-old voter who spoke on the condition that only his first name be used because he feared retribution, said he arrived at 11 a.m. Saturday at his polling station at Saburi Primary School in Abuja, the capital. He found hundreds waiting.
The military was called in three hours later to help organize the line, Jude said, but by 9:30 p.m., he had still not voted and the officials shut down the voting, saying they needed to start the counting. They promised to come back the next day so that those who had not yet voted could do so. But Jude said that when he returned to the school on Sunday, no officials were there.
“That was how about 500 persons were disenfranchised in that polling unit,” Jude said on Tuesday.
“This is my first time of trying to vote in this country,” he added. “I’m being denied that — my right.”
Observers pointed to problems with a new digital voting system, which they said had not transmitted votes to the election commission’s website at the expected pace.
“Everybody was hoping that all the results would be uploaded on the I.N.E.C. website,” said Michael Famoroti, the head of intelligence at Stears, a data and intelligence company that is observing the vote. “Instead, it’s a hybrid of manual and electronic transmission.”
Idayat Hassan, the director of the Abuja-based Center for Democracy and Development, cited various problems with the vote, including the late arrival of officials to some polling stations on Saturday and the failure to quickly upload results.
“It has weakened public perception of transparency and accountability instead of strengthening it,” she said.
With Mr. Tinubu leading in the vote count, Mr. Obi’s supporters in Lagos were trying to come to terms with the prospect of another term with an aging president from the governing party — the current leader, Mr. Buhari, is 80 and has suffered from numerous health problems.
At a restaurant in the upscale area of Ikoyi, Deborah Chukwuka, a 24-year-old waitress, said she regretted not having registered to vote in time.
Her colleague, Josephine Joseph, said she voted for Mr. Obi, but she was under no illusions: her candidate did not have the political support needed across the country to win the election, she said.
As the women waited for the last few clients to finish eating so they could close the restaurant, they refreshed their phones, looking for the latest results.