ABUJA (Reuters) - Tens of millions of Nigerians voted on Saturday in the most credible presidential election for decades, with very early results from a handful of polling stations showing President Goodluck Jonathan ahead. From the tin-roofed shacks of the Niger Delta, where Jonathan cast his vote, to the dusty alleyways of Daura, the northern home village of his main rival, ex-military ruler Muhammadu Buhari, voters came out en masse. In the sprawling commercial hub of Lagos, where many polling stations finished early, voters stayed on to watch the count, shouting out the total as polling agents tallied the ballots. "The politicians should know if they don't perform they are going to be voted out," said businessman Ahibuogwu Brian among the populous lagoon-side shanties of Makoko. "The electorate now know we have the power to chose our leaders." The polls pit Jonathan , the first head of state from the oil-producing Niger Delta, against Buhari, a northern Muslim with a reputation as a disciplinarian. Results from around a dozen polling units gave Jonathan a comfortable lead in Lagos, where his ruling party performed weakly in parliamentary elections last week. It was a similar story in the Niger Delta and parts of the southeast. But a stronger overall turnout in the north, where Buhari is popular, could make it a close race. Jonathan needs a simple majority and a quarter of the vote in two thirds of the 36 states to win in the first round. Buhari was in front in most of around 40 polling units visited by Reuters in the northern city of Kano, although Jonathan was generally the runner-up. He may however struggle to reach 25 percent in Buhari's home state of Katsina. There are more than 73 million registered voters and 120,000 polling stations. Final results could take days. Across most of the country of 150 million there was little sign of the chaos and violence that has dogged past elections although two bombs panicked voters in the troubled northeastern city of Maiduguri. There were no reports of casualties. There were reports of underage voting and attempts at ballot-stuffing in some areas. In the northern state of Bauchi irate youths torched an electoral commission office after officials were allegedly found thumbprinting ballot papers. "There are concerns that need to be addressed, but overall this is much better than the past," said Clement Nwankwo, head of the Policy and Legal Advocacy Centre (PLAC) in Abuja, working with more than 20 civil society groups to monitor the vote. "We have not seen large-scale reports of malpractice, nor of collusion between electoral officials and politicians." President Jonathan , a former zoology teacher born to a family of canoe makers, is the favourite. He is backed by the national machinery of the People's Democratic Party (PDP), whose candidate has won every presidential race since 1999. "For economic reasons and to reduce tension, we pray that whoever will win should win at the first ballot," Jonathan said after casting his vote in the Niger Delta. But Jonathan is resented by some in the north, who believe he is usurping the right of a northerner to the presidency for another four years. He inherited office after his predecessor, northerner Umaru Yar'Adua, died last year in his first term, interrupting a rotation between north and south. Buhari, a strict Muslim known for his "War Against Indiscipline," is hoping to capitalise on some of the resentment and is likely to win strong northern support despite his Congress for Progressive Change (CPC) being a young party. The former general told Reuters he feared the ruling party was trying to manipulate the vote out of desperation. "They could do anything and they are trying everything but luckily people are very sensitive this time around and they are determined to make their vote count," he said. Fellow opposition contender Nuhu Ribadu's Action Congress of Nigeria (ACN) party has its stronghold in the southwest, and could help force a run-off. But the two failed to agree a last minute alliance this week, leaving the anti-Jonathan vote split.