The Nigerian Red Cross says almost 50,000 people have fled from their homes following post-election violence.
Riots broke out in the north after Goodluck Jonathan, a southerner, emerged as the winner of the presidential poll.
A civil rights group says the unrest has left more than 200 dead, while hundreds of arrests have been made.
A Red Cross spokesperson told the BBC that the number of displaced trebled on Wednesday from from 16,000 to 48,000, mainly in the north.
Nigeria is divided by rivalry between the predominantly Muslim north and the mainly Christian south.