Nigerians headed to the polls Saturday to elect a new president in a knife-edge vote against a backdrop of security fears which escalated when Boko Haram appeared to carry out its pledge to disrupt the election, attacking two polling stations.

At least two people were killed in the attacks in the northeastern villages of Birin Bolawa and Birin Fulani.

"We could hear the gunmen shouting, 'Didn't we warn you about staying away from (the) election?'," an election official who witnessed the shooting said requesting anonymity.

According to FRANCE 24’s Nicolas Germain in Nigeria, some 360,000 police officers had been deployed to secure voters’ safety ahead of the poll following the threats from Boko Haram.

“There are fears for this day and also for when the results will be announced, which will probably be on Monday,” he said.

Nigeria's electoral commission said it would extend voting into Sunday in polling stations that had technical issues with biometric card-reading machines.

"In polling units where accreditation was suspended to the following day, in accordance with the existing guidelines, arrangements will be made for voters to vote tomorrow," commissioner Chris Yimoga told journalists in Abuja.

Incumbent President Goodluck Jonathan is seeking a second four-year term as leader of Africa's most populous nation against a strong challenge from the main opposition candidate Muhammadu Buhari.

The vote has been seen as a referendum on Jonathan's record over the past four years, with an escalation in the Boko Haram insurgency and the continent's top economy hit by the global shock in oil prices.

Election postponed

The election was postponed from February 14 because of military operations against Boko Haram in the northeast, which has since seen a series of claimed successes against the militants.

Many people had formed queues outside polling stations since the early hours or even slept overnight.

The Muslim-majority north is generally seen as a stronghold of Buhari and his All Progressives Congress (APC) opposition.

Jonathan and his Peoples Democratic Party (PDP) are viewed as having larger support in the mainly Christian south.

In the president's home town of Utuoke, Bayelsa state, Laurence Banigo, a 42-year-old civil engineer, said: "This is a great day for our son, and we are set to return him to power.

"He has done well. He deserves a second term."

In Buhari's hometown of Daura, in the northern state of Katsina, voter Moustapha Osman highlighted the security problem that has blighted Jonathan's presidency.

"We are ready 100 percent to vote, to vote the candidate that will protect our lives and integrity of this country," he said.

Dozens have been killed in pre-election violence, al though leading candidates signed a peace pledge. Some 1,000 people were killed in rioting after Buhari lost to Jonathan in 2011.

(FRANCE 24 with REUTERS, AP, AFP)