His main challenge is expected to come from Muhammadu Buhari, an ex-military leader popular in the north.Before voting began, there were two explosions in the city of Maiduguri, though no injuries have been reported.The polls close at 1700 (1600 GMT), but those already in the queue will be able to cast their vote, no matter how long it takes.
According to the law, counting should start immediately at the polling stations after everyone has voted.With voting now under way across the country the early signs are encouraging; the organisation of this poll seems to have gone well.In the relative cool of the early morning, long lines of voters began forming at the Sadiya Uku polling station here in Kano, the biggest city in the north.A nearby main road to the airport, usually choked with cars and motorbikes, was virtually empty as residents obeyed the injunction not to drive on voting day.
After presenting cards for verification, each voter is required to return later in the day to actually cast their vote. It’s a slow process that will take most of this long, hot day.But everyone is expressing the fervent hope that this poll with pass off peacefully and that the cheating and blatant ballot-rigging of previous polls are kept to a minimum this time.After voting, he said the election was a “new dawn in Nigeria’s political evolution”.
“If the ballot paper means nothing then there is no democracy… Nigeria is now experiencing true democracy where we the politicians have to go to the people.”
Although the president enjoys huge popularity in the south of the country, he is sometimes characterised as a technocrat lacking in charisma.
He said he was confident of victory, but asked if he would leave office if he lost, he replied: “Of course.”
He said he hoped there would not be a run-off because elections cost a “colossal sum of money”.
“For economic reasons and to even to reduce tensions we pray that whoever should win should win at the first ballot.”
Africa’s largest oil producer has long been plagued by corruption and has a history of vote fraud and violence.
In north-eastern Maiduguri, an explosion tore through the election commission’s local office on Friday night, and there was another blast at a police station early on Saturday.
The city, in Borno state, was also hit by bomb blasts during the parliamentary election a week ago.
But elsewhere in Borno – one of Nigeria’s poorest areas – officials said the voter registration process was running smoothly.
“Everything’s going well. People are co-operating, there is security, there are ballot papers. I think this is best election ever,” a presiding officer told the BBC.
Voters expressed hope that the election would be fairer than previous votes.Williams Beacher, a voter in Kano, said he had confidence in the new election chiefs.
“In previous elections, before we finish casting our vote, the national result had already been announced,” he said.
Allegations of ballot-stuffing plagued the 2007 election, which brought Mr Jonathan to power as the vice-president.
He took over as president in 2010 when the incumbent died, becoming the first leader from the oil-producing Niger Delta region.
His other main challengers for the presidency are former anti-corruption chief Nuhu Ribadu and Kano state governor Ibrahim Shekarau, though both are seen as rank outsiders.
Mr Jonathan’s People’s Democratic Party lost seats in a parliamentary election last week.
But he remains favourite in opinion polls, and his chances have been boosted after Mr Buhari and Mr Ribadu failed to agree a formal alliance to run against him.
The relatively successful conduct of the parliamentary election has increased confidence in the ability of the electoral commission, Inec, to ensure a fair presidential vote.However, bomb blasts and other attacks killed dozens in the run-up to the polls.
With 74 million registered voters, Nigeria has the biggest electorate on the continent.
The head of the African Union’s observer mission, former Ghanaian President John Kufuor, said some shortcomings had been found with the election process but he was confident the electoral commission would resolve them.
“If Nigeria gets it right, it will impact positively on the rest of the continent and show the rest of the world that Africa is capable of managing its electoral processes,” said Mr Kufuor.
“If Nigeria gets it wrong, it will have a negative influence on the continent with dire consequences.