Nigeria extended voting to Sunday because of technical glitches as millions turned out to vote in a presidential election that analysts say is too close to call.

Nearly 60 million people have cards to vote, and for the first time there is a possibility that a challenger can defeat a sitting president in the high-stakes contest to govern Africa's richest and most populous nation.

The front-runners among 14 candidates are President Goodluck Jonathan and former military dictator Muhammadu Buhari.

Voters also are electing 360 legislators to the House of Assembly, where the opposition currently has a slight edge over Jonathan's party.

Nigeria's political landscape was transformed two years ago when the main opposition parties formed a coalition and for the first time united behind one candidate, Buhari.

Polling will continue Sunday in some areas where new machines largely failed to read voters' biometric cards, said Kayode Idowu, spokesman of the Independent National Electoral Commission. That includes some areas of Lagos, a megacity of 20 million and Nigeria's commercial capital on the Atlantic coast.

In other areas, vote counting ended Saturday night, with blackouts that are routine forcing some officials to count by the light of vehicles and cellphones.

Earlier, Boko Haram extremists waving guns forced voters to abandon polling stations in three villages of northeastern Gombe state, witnesses said. Nigeria's home-grown militants have vowed to disrupt elections, calling democracy a corrupt Western concept.

Two car bombs exploded at two polling stations in southeast Enugu state but did not hurt voters, police said. Police detonated two other car bombs at the scene of the first explosion, a polling station set up at a primary school, said Enugu state police Commissioner Dan Bature. Boko Haram has been blamed for many car bombings but was not immediately suspected in the southeastern blasts far from its northeast stronghold.

Jonathan denied the attacks, saying the state governor told him there were no blasts.

The oil-rich and heavily populated south that traditionally votes for Jonathan's party is deeply contested this time and has become a political battleground.

The official website of the Independent National Electoral Commission was hacked but was quickly secured, said officials who said the site holds no sensitive material.

Thousands of people forced from their homes by the Islamic uprising lined up to vote at a refugee camp in Yola, capital of northeast Adamawa state, which is hosting as many refugees as its 300,000 residents.

Refugee Elzubairu Ali does not know when she will be able to return to her home.

"We have to wait for the time when the Nigerian army will totally wipe them (Boko Haram) out before we can go back," she said after voting.

Nigeria's military announced Friday it had destroyed the headquarters of Boko Haram's so-called Islamic caliphate and driven the insurgents from all major areas in northeast Nigeria. There was no way to verify the claim, which seems unlikely. Critics of Jonathan have said recent military victories after months of ceding territory to the Islamic extremists are a ploy to win votes — a charge the presidential campaign denies.

The failure of Jonathan's administration to curb the insurgency, which killed about 10,000 people last year, has angered Nigerians in the north.

International outrage has grown over another failure — the rescue of 219 schoolgirls kidnapped by Boko Haram nearly a year ago. The extremists have abducted hundreds more since then, using them as sex slaves and fighters.

On Saturday, the voting process began late in most places. Officials rushed across the country delivering ballot materials by trucks, speedboats, motorcycles, mules and even camels, in the case of a northern mountaintop village.

Good humor turned to anger and altercations as people waited hours and temperatures rose up to 100 degrees (37 degrees Celsius), only to find that machines were not reading new biometric voting cards.

Even the president was affected. Three newly imported card readers failed to recognize the fingerprints of Jonathan and his wife. Biometric cards and readers are being used for the first time to discourage the kind of fraud that has marred previous votes.

Afterward, Jonathan wiped sweat from his brow and urged people to be patient as he had, telling Channels TV: "I appeal to all Nigerians to be patient no matter the pains it takes as long as if, as a nation, we can conduct free and fair elections that the whole world will accept."

Jonathan cast his ballot later in the day.

Social media was abuzz with the problem. One tweeter said they solved their issue by having an official remove the protective plastic film from the screen to read a fingerprint on the card reader.

This is only the eighth election since Nigeria's independence from Britain in 1960, because of decades of military dictatorship that ended in 1999.

Nigeria is beset by violence. In addition to the Islamic uprising, there are militants demanding a better share of oil revenues who attack petroleum installations in the south and deadly land disputes across the middle of the country between semi-nomadic Muslim cattle herders and mainly Christian farmers.

"We need many changes in Nigeria," government worker Lawal Dahiru said in Buhari's home town of Daura. "We have security problems, no job opportunities, we need infrastructure like roads, electricity, water supply, and to mechanize our agriculture."

Nervous foreign investors are watching as Nigeria is Africa's largest destination for direct foreign investment though its oil-dependent economy is hurting from slashed petroleum prices.

The Islamic uprising has exacerbated relations between Christians like Jonathan, who dominate the oil-rich south, and Muslims like Buhari who are the majority in the agricultural and cattle-herding lands of the north. The population of 170 million is almost evenly divided between Christians and Muslims.

Some 1,000 people were killed in rioting after Buhari lost to Jonathan in the 2011 elections. Thousands of Nigerians and foreign workers have left the country amid fears of post-election violence.

In 2011, there was no doubt that Jonathan had swept the polls by millions of votes.

Now the race is much closer.

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