ABUJA, Nigeria — Nearly two hours after voting in Nigeria’s presidential election officially opened on Saturday, a poll worker grabbed Florence Michael’s thumb, ready to stamp her fingerprint so, finally, she could vote.
Her thumb hovered over the ink pad before he pushed her hand back and told her to wait. Again. Workers at the sidewalk polling station along Gana Street — blocks from election officials’ headquarters here in the capital, Abuja — were not quite ready for business.
It was yet another delay in the already delayed elections in Nigeria, Africa’s biggest economy, and one of many scenes of exasperation among already frustrated voters. Last weekend, officials had postponed the vote by one week, citing logistical issues. That decision came in the middle of the night, hours before polls were to open.
President Muhammadu Buhari, who led Nigeria under military rule in the 1980s, has promised to continue a crackdown on corruption that helped him gain office in 2015, the country’s first peaceful democratic transfer of power. He is being challenged for a second term by more than 70 candidates, including his main rival, Atiku Abubakar, a former vice president and perennial candidate.
Mr. Abubakar, facing allegations of corruption, has promised to create jobs — a potent pledge to an electorate consumed by concerns about unemployment — and to shore up Nigeria’s fragile economy, which is slowly recovering from a recession.
Worries about security, which is deteriorating in many parts of the country, hung over some areas where the tightly contested election could spark violence after results are announced as early as Monday. Both leading candidates are from the north, and many experts worried about whether a losing party would peacefully accept the results.
On Saturday night, Mr. Abubakar’s aides seemed to be spoiling for a fight, making allegations of irregularities before results were tabulated.
Analysts expected a lower turnout Saturday than if the election had taken place last weekend. Nigeria has no absentee voting, and many people must travel long distances to cast ballots in their home district where they are registered.
Having made that journey last weekend, many left after the vote was postponed, with no plans to return.
Mr. Buhari announced a drop in the price of fuel to encourage voters to travel again to vote and declared Friday a national holiday. But here in Abuja, many hotel workers did not vote because they were working double shifts to serve the hundreds of election observers in town.
To calm fears of voter fraud, Mr. Buhari said earlier in the week that anyone who tried to rig the vote could expect to be killed by security forces.
Mr. Buhari’s critics say that he has fought graft only when it helps him politically and that he has failed to deliver on his campaign promise to defeat Boko Haram, an Islamist insurgency that has ravaged the northeast of the country for almost a decade.
Two hours before the polls were to open at 8 a.m. Saturday, Boko Haram had already sent a chilling reminder that it is far from defeated. Bomb blasts and gunfire were reported in scattered areas across the outskirts of Maiduguri, Boko Haram’s founding city, in the northeast.
Residents took cover in their homes; some had been scared off from voting. Government officials initially announced to a skeptical electorate that the blasts were part of a military drill before later conceding that militants were responsible. Boko Haram’s faction loyal to the Islamic State said later that it was responsible.
In Rivers State, six people and one soldier were killed when troops patrolling the area on election day were ambushed, an army spokesman said.
In the country’s largest city, Lagos, violence broke out at several polling stations. Thugs threw bottles, injuring several people.
By 11:30 a.m., a quarter of polling stations across the country still had not opened, according to YIAGA Africa, a pro-democracy nonprofit group that sent 3,000 monitors into polling stations.
In Yobe State, YIAGA Africa said, observers weren’t allowed to perform their official duties, and in Rivers State election materials were snatched at several polling stations.
In the northeast, aid workers reported busloads of displaced people had arrived at countryside encampments, saying they had been rounded up by government officials who paid them the equivalent of $6 to return home and vote for specific candidates.
In Lagos, high-tech card readers plagued one polling station. One failed to recognize both the card and the thumbprint of Ebele Helen Odigie, who looked despondent as she was turned away. Workers tried 22 times without success to get a reader to recognize the voting card of Ayokunle Fashola, but she was allowed to vote anyway.
At the Living Water polling unit in Kubwa, just outside Abuja, voting proceeded but a security officer seized phones of anyone who snapped a photo while in line. That included Chibuzor Bonaventure who was taking a selfie. At age 27, he is among 51 percent of the country’s 84 million registered voters between the ages of 18 and 35.
Just down the road at a school compound in Kubwa, voting began on time, card readers worked and people calmly queued in orderly lines, casting ballots inside cardboard voting booths.
That wasn’t the case on Gana Street in Abuja, a neighborhood of walled villas, international banks and embassies where grumbling voters swirled about, confused over when voting would actually start, two hours after the station officially opened.
Election officials weren’t much help. They herded more than 400 people together to write their names and voter numbers on slips of paper, then told them to check their names against a list taped to a wall across the street. Shouts erupted.
“What is wrong in this country!” one man yelled.
Finally, voters were organized alphabetically into queues. Several line jumpers prompted more shouting. Things seemed to settle down, then women voters decided they didn’t want to queue with men. New lines formed. New shouting broke out.
Younger voters made way for Ms. Michael, a 71-year-old food seller, who moved to the front of the line.
“The election has opened,” a worker loudly announced at 9:26 a.m. “Voting has started.”
A hush fell over the crowd. Ms. Michael ducked under a string holding back voters from the registration table.
“No! Not yet!” a worker barked at her.
Eventually, Ms. Michael was allowed to cast her vote, for Mr. Buhari. By the end of voting more than 500 people had cast ballots at the Gana Street station, which had nearly emptied out even before it officially closed.
A dozen men remained, clustered under the shade of a wide, yellow flowering tree and hovering over a single smartphone. Each said he hadn’t asked the others whom they supported. The subject was too heated. Instead, they were checking friends’ Facebook accounts to see how voting was going elsewhere.
“We want to vote and return home safely,” said Olajide Taiwo, a land surveyor. “We believe in Nigeria.”