Thousands of armed police and soldiers were drafted to Delta state for the re-run election, held after a court in 2010 overturned the 2007 victory of governor Emmanuel Uduaghan, a member of the ruling People’s Democratic Party (PDP).
Delta is one of three main states in the Niger Delta, the heartland of Africa’s biggest oil and gas industry and a restive region seen as a potential flashpoint during presidential and parliamentary elections in April.
The Independent National Electoral Commission (INEC) acknowledged problems, including omissions on the voter register and the late arrival of election materials, but said they were not enough to call the credibility of the poll into question.
INEC chairman Attahiru Jega, who travelled from Abuja to monitor the process, said: â€œWe have done our best. We have learnt a lot of lessons in this re-run which will prepare us for the general elections.â€
Results were expected early on Friday.
Journalists saw a group of unarmed youths attempt to hijack a minibus carrying electoral materials in the centre of Warri shortly before polling began. The journalists were chased away by the mob.
Opposition supporters also complained of intimidation.
Benjamin Amioku, a polling agent from the opposition Democratic People’s Party, told reporters: â€œThe (voting) materials arrived accompanied by about 13 people who asked me who I was.
â€œThey slapped me for no reason, I had to run for my life. I lost my cellphone and shoe in the process of being beaten.â€
There were also reports of ballot box snatching in other areas, but Delta state police spokesman Charles Muka said there had been no serious unrest and that everything had been â€œpeaceful beyond our imaginationâ€.
About 25 000 police officers, including armed anti-riot police, as well as soldiers and bomb disposal experts were on hand to try to ensure the vote passed peacefully.
President Goodluck Jonathan, who is from the Niger Delta, flew from Abuja on Tuesday to support Uduaghan’s campaign. But Uduaghan is not a universally popular figure and security experts fear unrest if he is declared winner of the polls.
Nigeria has been shaken by violence in recent weeks, including a New Year’s eve bomb blast on the edge of an army barracks in Abuja, a week after a series of blasts and subsequent clashes killed 80 in the central city of Jos.
Political rallies have also turned violent in some areas.
Police said on Thursday PDP Senate majority leader Teslim Folarin and three of his aides had been charged with involvement in
the murder of a trade union activist during violence at a rally in the southwestern city of Ibadan last week.
Home-made bombs hit a rally in Bayelsa state, next to Delta, on December 29 and there are fears the oil region could flare up again ahead of the April polls.
Warri was hit by twin car bombs in March 2010 during talks about implementing an amnesty programme for militants brokered by Jonathan.
Jonathan is the first Nigerian president from the Ijaw ethnic group, the largest in the Niger Delta, and his failure to win the ruling party primaries next week or the April polls could trigger unrest in his home region.
But his election bid is contentious because he is a southerner. Some in the ruling party say an agreement about power sharing among Nigeria’s regions meant the next president should be a northerner.
The PDP has been the dominant party in Nigerian politics since the end of military rule more than a decade ago, controlling more than two-thirds of the country’s 36 states.
Several PDP governors including Uduaghan have had their 2007 elections overturned by the courts in recent months.
The polls four years ago were so marred by violence and intimidation that observers declared them not to have been credible and legal wrangling dragged on in some cases for years. Nigeria is hoping to avoid a similar fiasco in April.
Uduaghan faces 13 challengers including Great Ogboru of the Democratic People’s Party and Ovie Omo of the Republican Party of Nigeria, seen as his two main rivals. â€“ Reuters.