Vote buying has been observed by election monitors from NGO the Centre for Democracy and Development (CDD)
The CDD is one of the main pro-democracy organisations in Nigeria and is considered very credible.
Their preliminary report on the election says "unfortunately, there were many areas where vote buying was observed".
In Enugu state its team saw some men collecting money outside a polling station after they had cast their votes.
In Osun state, CDD monitors observed people writing their names down after they had voted so that they could be given money, although observers didn't see the exchange of cash.
In Bayelsa state they observed party agents promising to contact voters later, implying that they will get paid at a later date.
Overall, the CDD said it was "pleased to note that elections are going on across the country, and there is significant turnout of voters".
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