The US and the UK have expressed concern about political interference in Nigeria’s elections as presidential challenger Muhammadu Buhari recorded huge victories in key northern states.
Mr Buhari, a northern Muslim is going up against incumbent Goodluck Jonathan, who is a Christian from the south of the country.
The challenger won 1.9 million votes in Kano against 216,000 for Jonathan and recorded victories in other northern states, however it is too early to forecast a result, in one of the most closely contested elections in years.
The United States and Britain said that after the vote there were worrying signs of political interference in the centralised tallying of the results.
"So far, we have seen no evidence of systemic manipulation of the process," U.S. Secretary of State John Kerry and British Foreign Secretary Philip Hammond said in a joint statement.
"But there are disturbing indications that the collation process - where the votes are finally counted - may be subject to deliberate political interference," they said.
The United Nations and the African Union, which both had election observers on the ground, said the vote was broadly in line with "continental and regional principles".
"The AUEOM (African Union Election Observation Mission) encourages all parties to resort to legally established channels, should there be a dispute on the outcome of the process," it said in a statement.
"The AU long-term observers will continue to observe the post-electoral process."