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.