Partial results from Nigeria’s election give ex-military ruler Muhammadu Buhari a substantial lead over the incumbent, President Goodluck Jonathan.
With only five states left to declare, Gen Buhari’s All Progressives Congress (APC) is ahead by almost three million votes.
A victory for Gen Buhari would make President Jonathan the first incumbent to lose an election in Nigeria.
Correspondents say it is likely the loser will allege foul play.
More than 800 people were killed in protests after Mr Jonathan beat Gen Buhari in the previous election.